News – Page 2 – Narrabay

Trolls In the Narragansett Bay: Adventures in Bacteria sampling

Most people picture Narragansett Bay as calm, sparkling, and post card-perfect. But if you’ve ever been out there in a small boat with a cooler full of sample bottles and a mission to track down bacteria data, you should know the truth: the bay has trolls.

Every other week, we’re out on the bay collecting water samples to test for bacteria. Why? Because the health of Narragansett Bay isn’t just about how pretty it looks, its about what’s living in it, and sometimes, what’s floating in it that shouldn’t be. Bacteria levels can mean the difference between a thriving shellfish industry and a “DO Not Harvest” sign. Our data helps protect public health, the environment, and the economy.

Why would trolls be out in the bay, you ask? A few theories staff have in mind. Perhaps trolls follow the plankton blooms. Scientist track all sorts of information, why not troll movement. Trolls may have a curiosity about science and wants to see what we are doing. Water sampling is fascinating! Finally we think the trolls like a good swim in the Narragansett Bay. So, next time your out on the bay and something catches your eye, don’t be too quick to dismiss it. It just might be …a troll!

June 23 – June 29, 2025

Phillipsdale Landing

Overall, water quality at Phillipsdale Landing was poor to good this week. Weather conditions were relatively dry this week, with a total of 0.07 inches recorded at T.F. Green, and the majority of rainfall occurring on the 26^th. Blackstone River flow decreased slightly over the course of the week, and remained below the 20-year daily median flow. Salinity at the surface averaged 20.6 ppt and ranged from 14.3 ppt to 25.3 ppt. At the bottom, salinity averaged 23.4 ppt and ranged from 4.6 ppt to 27.2 ppt. Temperatures this week averaged 22.3 °C at the surface and 21.4 °C at the bottom. Surface temperatures ranged from 19.8 °C to 26.4 °C, while bottom temperatures ranged from 19.4 °C to 24.6 °C.

Dissolved oxygen (DO) at Phillipsdale Landing remained above the hypoxia threshold (i.e., DO >2.9 mg/L) for most of the week. Hypoxic conditions were observed at the surface briefly during early morning on June 27^th and June 29^th. Hypoxic conditions were observed at the bottom for multiple hours in the early morning of June 27^th, briefly in the evening of June 28^th, and for multiple hours in the evening of June 29^th. Surface DO averaged 7.3 mg/L and ranged from 2.8 to 15.1 mg/L. Bottom water DO concentration averaged 5.3 mg/L and ranged from 2.3 mg/L to 12.3 mg/L. Chlorophyll ranged from low to elevated levels throughout the week, averaging 22.2 ug/L at the surface and 16.1 ug/L at the bottom, with evidence of moderate phytoplankton blooms occurring throughout the week. Maximum surface chlorophyll readings reached 92.1 ug/L on the early morning of June 27^st. Please note that tidal fluctuations and Blackstone River flows greatly influence water column salinity, temperature, and DO at this location.

Bullock Reach

Sondes were swapped this week on June 24^th. Overall, water quality ranged from fair to good at Bullock Reach this week. Salinity averaged 26.1 ppt, 28.4 ppt, and 30.4 ppt at the surface, middle, and bottom sondes, respectively. Surface salinity ranged from 22.2 to 29.1 ppt, mid salinity ranged from 24.9 to 30.6 ppt, and bottom salinity ranged from 28.4 to 31.4 ppt. Surface temperature averaged 22.6 °C and ranged from 20.2 °C to 26.5 °C. Mid temperatures averaged 21.1 °C and ranged from 19.2 °C to 24.6 °C. Bottom temperatures averaged 19.1 °C and ranged from 17.4 °C to 20.6 °C.

DO at Bullock Reach remained above the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week. Surface DO averaged 7.6 mg/L and ranged from 5.1 to 11.3 mg/L. In the mid waters, DO averaged 6.0 mg/L and ranged from 3.9 to 9.7 mg/L. At the bottom, DO averaged 4.9 mg/L and ranged 3.9 to 6.3 mg/L. Chlorophyll readings ranged from low to moderate, with evidence of moderate phytoplankton blooms occurring throughout the week. Readings averaged 10.1 µg/L at the surface, 12.5 µg/L at mid-depth, and 9.8 µg/L at the bottom. The maximum surface chlorophyll was 42.7 µg/L on the afternoon of June 28^th.

July 8, 2025

Phytoplankton samples were collected on July 8, 2025 at Bullock’s Reach and analyzed in the laboratory shortly after collection.

It was sunny, hot, and humid on this day. The water temperature was 25.24 °C, the salinity was 27.85 psu, and the chlorophyll a was 5.55 ug/L.

The qualitative tow net sample had a quick filtration time. The filtrate contained seaweed and particulates and had a reddish brown coloration.

The analysis of the quantitative whole water sample revealed a total of 875,000 cells/L. The microflagellates were found at 268,000 cells/L. The most predominant phytoplankton genera were Prorocentrum spp. at 284,000 cells/L , and Thalassiosira spp. at 198,000 cells/L.

200x phase contrast micrograph of Monogonontan Rotifer

Rotifers of the subclass Monogononta are common metazoans found in freshwater, brackish and marine environments. Although they are small, ranging in size from 50–500 µm, they are extremely important in the transfer of energy from algae, microbes, and detritus to higher trophic levels in community food webs.

June 16 – June 22, 2025

Phillipsdale Landing

Sondes were swapped this week on June 17^th. Overall, water quality at Phillipsdale Landing was fair to good this week. Weather conditions were slightly drier than the previous week, with a total of 0.21 inches recorded at T.F. Green, and the majority of rainfall occurring on the 17^th. Blackstone River flow remained near the 20-year daily median until the end of the week, when flows declined below the 20-year daily median values. Salinity at the surface averaged 13.1 ppt and ranged from 3.1 ppt to 21.7 ppt. At the bottom, salinity averaged 21.5 ppt and ranged from 3.1 ppt to 27.9 ppt. Temperatures this week averaged 21.1 °C at the surface and 19.0 °C at the bottom. Surface temperatures ranged from 17.7 °C to 25.6 °C, while bottom temperatures ranged from 16.0 °C to 22.4 °C.

Dissolved oxygen (DO) at Phillipsdale Landing remained above the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week. Surface DO averaged 9.0 mg/L and ranged from 4.4 to 17.1 mg/L. Bottom water DO concentration averaged 5.6 mg/L and ranged from 3.9 mg/L to 10.4 mg/L. Chlorophyll ranged from low to moderate levels throughout the week, averaging 21.4 ug/L at the surface and 17.1 ug/L at the bottom. Maximum surface chlorophyll readings reached 92.1 ug/L on the morning of June 21^st. Please note that tidal fluctuations and Blackstone River flows greatly influence water column salinity, temperature, and DO at this location.

Bullock Reach

Overall, water quality ranged from fair to good at Bullock Reach this week. Salinity averaged 24.7 ppt, 26.8 ppt, and 29.9 ppt at the surface, middle, and bottom sondes, respectively. Surface salinity ranged from 21.5 to 26.6 ppt, mid salinity ranged from 23.6 to 28.7 ppt, and bottom salinity ranged from 27.9 to 31.0 ppt. Surface temperature averaged 20.6 °C and ranged from 18.3 °C to 23.4 °C. Mid temperatures averaged 19.5 °C and ranged from 16.5 °C to 22.7 °C. Bottom temperatures averaged 16.7 °C and ranged from 15.1 °C to 20.1 °C.

DO at Bullock Reach remained above the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week. Surface DO averaged 9.5 mg/L and ranged from 7.0 to 12.8 mg/L. In the mid waters, DO averaged 7.5 mg/L and ranged from 4.9 to 9.7 mg/L. At the bottom, DO averaged 4.7 mg/L and ranged 3.6 to 6.7mg/L. Chlorophyll readings ranged from low to elevated, with evidence of moderate phytoplankton blooms occurring throughout the week. Readings averaged 18.2 µg/L at the surface, 18.2 µg/L at mid-depth, and 6.5 µg/L at the bottom. The maximum surface chlorophyll was 63.8 µg/L on the evening of June 20^th.

June 9 – June 15, 2025

Phillipsdale Landing

Overall, water quality at Phillipsdale Landing was fair to good this week. Weather conditions were slightly drier than the previous week, with a total of 0.31 inches recorded at T.F. Green, and the majority of rainfall occurring on the 10^th. The Blackstone River flow decreased throughout the week, exceeding the 20-year daily median until the 15^th. Salinity at the surface averaged 8.4 ppt and ranged from 2.8 ppt to 21.8 ppt. At the bottom, salinity averaged 20.1 ppt and ranged from 4.2 ppt to 27.9 ppt. Temperatures this week averaged 20.1 °C at the surface and 17.6 °C at the bottom. Surface temperatures ranged from 17.5 °C to 23.4 °C, while bottom temperatures ranged from 15.0 °C to 22.6 °C.

Dissolved oxygen (DO) at Phillipsdale Landing remained above the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week. Surface DO averaged 8.0 mg/L and ranged from 4.9 to 10.6 mg/L. Bottom water DO concentration averaged 5.1mg/L and ranged from 3.3 mg/L to 8.9 mg/L. Chlorophyll ranged from low to moderate levels throughout the week, averaging 8.1 ug/L at the surface and 10.1 ug/L at the bottom. Maximum surface chlorophyll readings reached 24.9 ug/L on the evening of June 13^th. Please note that tidal fluctuations and Blackstone River flows greatly influence water column salinity, temperature, and DO at this location.

Bullock Reach

The Bullock Reach Buoy sondes were deployed for the season on June 10^th, 2025. Overall, water quality ranged from fair to good at Bullock Reach this week. Salinity averaged 22.7 ppt, 26.8 ppt, and 30.5 ppt at the surface, middle, and bottom sondes, respectively. Surface salinity ranged from 15.4 to 26.4 ppt, mid salinity ranged from 21.7 to 29.8 ppt, and bottom salinity ranged from 29.0 to 31.5 ppt. Surface temperature averaged 19.0 °C and ranged from 17.0 °C to 20.9 °C. Mid temperatures averaged 17.7 °C and ranged from 15.5 °C to 20.3 °C. Bottom temperatures averaged 14.9 °C and ranged from 13.8 °C to 16.7 °C.

DO at Bullock Reach remained above the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week. Surface DO averaged 10.5 mg/L and ranged from 6.1 to 14.2 mg/L. In the mid waters, DO averaged 7.6 mg/L and ranged from 4.6 to 12.0 mg/L. At the bottom, DO averaged 4.9 mg/L and ranged 4.3 to 6.1mg/L. Chlorophyll readings ranged from low to elevated, with evidence of substantial phytoplankton blooms occurring throughout the week. Readings averaged 32.9 µg/L at the surface, 31.3 µg/L at mid-depth, and 6.0 µg/L at the bottom. The maximum surface chlorophyll was 78.7 µg/L on the evening of June 14^th.

June 2 – June 8, 2025

Phillipsdale Landing

Sondes were swapped this week on June 3^rd. Overall, water quality at Phillipsdale Landing was fair to good this week. Weather conditions included moderate rain, with a total of 0.56 inches recorded at T.F. Green, and the majority of rainfall occurring on the 7^th. The Blackstone River flow peaked on the 7^th, exceeding the 20-year daily median, before which flows remained near the 20-year daily median. Salinity at the surface averaged 3.6 ppt and ranged from 1.3 ppt to 7.1 ppt. At the bottom, salinity averaged 14.6 ppt and ranged from 2.7 ppt to 28.0 ppt. Temperatures this week averaged 20.6 °C at the surface and 17.8 °C at the bottom. Surface temperatures ranged from 16.3 °C to 24.7 °C, while bottom temperatures ranged from 14.2 °C to 23.2 °C.

Dissolved oxygen (DO) at Phillipsdale Landing remained above the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week. Surface DO averaged 9.0 mg/L and ranged from 6.3 -12.4 mg/L. Bottom water DO concentration averaged 5.9 mg/L and ranged from 3.6 mg/L to 10.0 mg/L. Chlorophyll was low in the beginning of the week, but then increased, averaging 6.2 ug/L at the surface and 9.2 ug/L at the bottom. Maximum surface chlorophyll readings reached 32.0 ug/L near midday on June 7^th. Please note that tidal fluctuations and Blackstone River flows greatly influence water column salinity, temperature, and DO at this location.

Bullock Reach

The Bullock Reach Buoy remains out of the water for the winter. EM will coordinate with RIDEM to redeploy the buoy in late spring-early summer.

July 30, 2025

On July 30th, 2025, twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers; five of these stations were also sampled for enterococci bacteria. In the five days prior to sampling, 1.91 inches of precipitation was recorded at TF Green. Overall bacteria counts were lower than during the previous sampling event.

Fecal coliform counts were higher in the Seekonk River, compared to the Providence River (geometric mean of 55 MPN/100 mL for the Seekonk River compared to 9 MPN/100mL for the Providence River) for sampling conducted on July 30th. The maximum count (930 MPN/100 mL) was measured at the Point St. Bridge sampling location.

Fecal coliform counts were lower in the Providence River, compared to the previous sampling on July 16th (geometric mean of 9 MPN/100 mL compared to 16 MPN/100 mL on 7/16). Fecal coliform counts were lower in the Seekonk River, compared to the previous sampling on July 16th (geometric mean of 55 MPN/100 mL compared to 82 MPN/100 mL on 7/16).

Enterococci results had an overall geometric mean of 14 MPN/100 mL. Enterococci counts ranged from <10 MPN/100 mL at most sites to 109 MPN/100 mL at Point St. Bridge.

The next scheduled sampling date is August 13th.

The table below lists the Rhode Island bacteria standards for primary contact and shellfishing established by the Rhode Island Department of Environmental Management (RIDEM). RIDEM defines primary contact as any recreational activities in which there is prolonged and intimate contact with water, involving considerable risk of ingesting water (e.g., swimming, diving, water skiing and surfing). Please note that the RIDEM bacteria standards are provided here for informational purposes only and are not intended to indicate official state compliance with primary contact or shellfishing standards.

Summary of Rhode Island Bacteria Standards for Saltwater Primary Contact and Shellfishing

	Fecal Coliform	Enterococci
Primary Contact¹	Geometric mean ≤50 MPN/100 mL <10% of samples >400 MPN/100 mL	Geometric mean ≤35 colonies/100 mL All samples ≤104 colonies/100 mL²
Shellfishing	Geometric mean ≤14 MPN/100 mL <10% of samples >49 MPN/100 mL³	NO ENTEROCOCCI CRITERIA

¹Fecal coliform primary contact criteria applied only when adequate enterococci data are not available; ²Single sample maximum criterion for determining beach swimming advisories at designated beaches as evaluated by the Rhode Island Department of Health; ³For a three-tube decimal dilution.

Table adapted from Rhode Island Water Quality Regulations (250-RICR-150-05-1); see regulations for complete details.

July 30, 2025

Surface chlorophyll data were collected on July 30, 2025, while the R/V Monitor was underway collecting nutrient samples in the Providence and Seekonk River estuary. The average chlorophyll concentrations were categorized as fair in all individual areas surveyed as well as in the overall survey area. Overall, chlorophyll ranged from 1.1 µg/L to 46.06 µg/L with an average of 10.06 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

July 23, 2025

Surface chlorophyll data were collected on July 23, 2025, while the R/V Monitor was underway collecting nutrient samples in the Providence and Seekonk River estuary. The average chlorophyll concentrations were categorized as good in the Seekonk River, and as fair in all other areas. The average chlorophyll concentrations were categorized as fair over all areas surveyed. Overall, chlorophyll ranged from 2.85 µg/L to 28.47 µg/L with an average of 7.25 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

July 2, 2025

Surface chlorophyll data were collected on July 2, 2025, while the R/V Monitor was underway collecting nutrient samples in the Providence and Seekonk River estuary. The average chlorophyll concentrations were categorized as poor in the Seekonk River, and as fair in all other areas. The average chlorophyll concentrations were categorized as fair over all areas surveyed. Overall, chlorophyll ranged from 1.47 µg/L to 145.88 µg/L with an average of 17.45 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.