Watershed and Water Quality

The Watershed Team tests water samples rangeing from the fresh water that feeds into Cohasset Harbor from the upper reaches of the watershed to the ocean water of Massachusetts Bay that that enters and exits our harbor twice a day. 

Students monitor dissolved oxygen, pH, temperature, salinity, chlorophyll-a, nitrates and enterococci bacteria. Students work with a variety of lab equipment, such as a Turner Designs fluorometer for nitrate analysis. Fluorometry is used in biochemistry for measuring the intensity of fluorescence and absorbance when light passes through a liquid (water sample). CSCR’s  analyses helps us understand if there is too much bio-chem productivity, for example, a condition that causes algae blooms and a subsequent reduction of oxygen (and life) in an ecosystem. 

For a look at the team’s 2023 Data, click here

pH Bench
Prepping Nitrate analysis

Description of Sites:

The Watershed Team studies four different sites relating to the Gulf River. Three of the sites, Shockmans, Bleakies, and Musquashicut are located directly on the Gulf River, while the fourth site, Hunters Pond, is located on a freshwater source that feeds into the Gulf River. Shockmans is located closest to the mouth of the river, and as you continue farther upstream you first run into Bleakies, then later Musquashicut. The freshwater source the Hunters Pond site sits on feeds into the Gulf River farther upstream from Bleakies.

Description of Analytes:

Enterococci is the bacteria that the team measures at our three marine sites: Shockmans, Bleakies, and Musquashicut. Since Hunters Pond is a freshwater site, E. coli bacteria is measured instead. Bacteria are quantified using an IDEXX Quanti-Tray system and are measured in MPN/100mL. MPN/100mL stands for most probable number per 100 milliliters, or in simple terms this is the amount of bacteria in the water. For Enterococci (Shockmans, Bleakies, and Musquashicut), the cut-off where the water becomes unsafe to swim in is 104 MPN/100mL. For E. coli the cut-off is 88 MPN/100mL.


The Watershed Team is trying to figure out the relationship between bacteria and rainfall levels. The current hypothesis is that short intermittent amounts of rainfall contribute to elevated amounts of bacteria, while consistent and high amounts of rainfall result in lower amounts of bacteria. However, the team is still studying the correlation between the two, and no conclusion has been reached.