Snapshot of the Bay

Historical News

Week of May 14 - 20, 2023

Phytoplankton Sampling

Phytoplankton samples were collected on May 18, 2023 at Bullock Reach and analyzed in the laboratory shortly after collection. It was a beautiful sunny day with little to no wind on Narragansett Bay. Floating dead algae were detected and the Secchi disk measured 2.2 meters. Sondes data revealed the surface water temperature was 14.23⁰C, salinity was 24.16 psu, and chlorophyll a was 3.63 ug/L. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a light brown color and had a medium filter time. The tow net sample was analyzed qualitatively for microorganisms using phase contrast microscopy. The whole water sample was analyzed quantitatively under 200x phase contrast microscopy. A Hensen Stempel pipette was used to accurately deliver 1ml of sample to a Sedge-wick Rafter chamber. This analysis revealed a total of 2,328,000 cells per Liter. The micro flagellates were found at 72,000 cells/L. The most predominant phytoplankton genus was Guinardia spp. at 1,108,000 cells/L. Other representative genera include Dactyliosolen spp., Skeletonema spp., Chaetoceros spp.

200x phase contrast micrograph of Guinardia.

Week of May 21 - 27, 2023

Bacteria Sampling

On May 24, twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers. Five of these stations were also sampled for enterococci bacteria. Precipitation in the five days prior to sampling totaled 3.04 inches as recorded at TF Green, most of which occurred on May 20.

The geometric mean of fecal coliform results for all sites was 73 MPN/100 mL compared to 23 MPN/100 mL on May 10. Overall, bacteria counts were higher in the Seekonk River and Providence River this week than during the previous sampling event on May 10. Fecal coliform counts were geomeans of 132 MPN/ 100 mL in the Seekonk River and 56 MPN/ 100 mL in the Providence River. The maximum count (430 MPN/100 mL) was measured at Narragansett Boating Center (Seekonk River) and Point St. Bridge (Providence River).

Enterococci results had an overall geometric mean of 13 MPN/100 mL. Enterococci counts ranged from non-detect at Phillipsdale Landing, South FP East, and Conimicut Point to 74 MPN/100 mL at Point St. Bridge.

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.

Week of May 28 - June 3, 2023

Water Column Clarity

Water clarity was measured at seven locations in the Providence River and Seekonk River estuaries on May 31. There was no precipitation recorded at TF Green in the five days prior to the survey. Secchi depth averaged 1.5 meters, compared to 1.3 meters on the previous survey (May 24). The lowest clarity this week (0.8 meters) was measured at Edgewood Shoal while the greatest clarity (2.2 meters) was measured at Pawtuxet Cove. There was no clear north-to-south gradient in water clarity among the sites this week.

Week of May 21 - 27, 2023

Water Column Clarity

Water clarity was measured at eight locations in the Providence River and Seekonk River estuaries on May 24. Rainfall totaling 3.04 inches was recorded at TF Green in the five days prior to the survey, most of which occurred on May 20. Secchi depth averaged 1.3 meters, compared to 2.0 meters on the previous survey (May 18). The lowest clarity this week (0.9 meters) was measured at Pomham Rocks and Edgewood Yacht Club while the greatest clarity (1.7 meters) was measured at Bullock Reach and Point St. Bridge. There was a general north-to-south gradient of increasing water clarity among the sites this week.

Week of May 14 - 20, 2023

Water Column Clarity

Water clarity was measured at seven locations in the Providence River and Seekonk River estuaries on May 18. There was no precipitation recorded at TF Green in the five days prior to the survey. Secchi depth averaged 2.0 meters, compared to 1.9 meters on the previous survey (May 10). The lowest clarity this week (1.4 meters) was measured at Pawtuxet Cove while the greatest clarity (2.6 meters) was measured at Phillipsdale Landing and India Point Park. There was no clear north-to-south gradient in water clarity among the sites this week.