The surface water quality classification for Roseland Lake is B/AA. Class B/AA means "water use intended for fish and wildlife, recreation or navigation." Roseland Lake does not meet the criteria for the target class, which is Class AA: existing or proposed drinking water supply, fish and wildlife habitat, recreational use (may be restricted), agricultural and industrial supply. Discharges to Class AA surface water are restricted to discharges from public or private drinking water treatment systems, dredging and dewatering, and emergency and clean water discharges.


An Impaired, Hypereutrophic Warm Water Lake

Algae bloom at Roseland LakeRoseland Lake is considered impaired for its designated use of recreation due to excessive nutrients, eutrophication and biological indicators. The 305(b) Assessed Waterbody History Reports for Roseland Lake lists it as impaired due to Nutrient/Eutrophication Biological Indicators in 2012, 2010, 2008 and 2006. It was listed as impaired due to non-native aquatic plants (exotic species), non-native fish/shellfish/zooplankton (noxious aquatic plants) and nutrients in 2004 and 2002. (Watershed Assessment, Tracking & Environmental Results, U.S. EPA)

It is eutrophic because it is highly enriched with the nutrients phosphorus and nitrogen. Historical Changes in Connecticut Lakes Over a 55-Year Period noted that Roseland was "a hypereutrophic lake with nutrient and chlorophyll-a levels greatly exceeding all other sites in the eastern uplands, and with severely low transparency....” Surveys done in between 1937-1939 and 1973-1973 indicated the lake was becoming considering even more eutrophic over time (Water Chemistry and Fertility of 23 Connecticut Lakes)

According to the Muddy Brook and Little River Water Quality Improvement Plan, Roseland is considered a eutrophic warm water lake because it becomes thermally stratified in the summer months. By June, the bottom layer becomes anaerobic (very low oxygen content.) It remains that way throughout the summer.

In an anaerobic state, bottom sediments release phosphorus. It was theorized that poor mixing potential would not make that phosphorus available to support plant growth until the fall overturn. At that time, normal flows would flush the excess nutrients out of the basin. Limited tributary sampling has indicated that even under low flow conditions, the tributaries contain nutrient loads sufficiently high enough to support nuisance algae growth.

A 1991 study by the US Geological Survey concluded that, even though nitrogen and phosphorus concentrations in sediment were relatively high, it is unlikely that a significant level of those nutrients becomes available to phytoplankton during the growing season due to this thermal stratification.

However, Roseland lake does suffer from chronic algae blooms. Potential sources of nutrients and other pollution at Roseland Lake are agriculture, waterfowl, and unknown.

Cyanobacteria has been detected on occasion at Roseland Lake. Some species - but NOT all - of cyanobacteria produce toxins. If a dog swims in teh lake during a toxic cyanobacteria bloom, gets the algae on its fur and licks it off, it can become sick or even die. Some research indicates a potential link between toxic cyanobacteria and ALS. In 2018, testing of the lake for toxic cyanobacteria is being conducted. (Read more about toxic blue-green algae.)

The overall susceptibility rating for contamination of the Little River is high. A 1978 report by the CT DEP theorized that, because there is a large upstream watershed contributing to a relatively small lake volume, Roseland Lake would be susceptible to high levels of algae and/or aquatic plants even without human influence.

The USGS conducted an extensive study of the Roseland Lake watershed in the period between 1980 and 1983 (Kulp, 1991). This study estimated that 427 tons of sediment were deposited in the lake annually during that time period. This study also notes internal nutrient loading as a potential problem in the Lake.

Read more about plans and steps that are being taken to prevent further pollution and to improve water quality at Roseland Lake


Water quality monitoring at Roseland Lake is conducted by the Town of Putnam Water Pollution Control Authority, the CT DEEP, volunteers working with the Eastern Connecticut Conservation District (ECCD), Connecticut College, and various researchers.

Read more about ECCD water quality monitoring in 2018.

The Roseland Terrace Association, Inc., has two community wells (the second was installed in 2018) on the southeast shore of Roseland Lake, and is required to periodically test the quality of their tapwater. Radon is present in the well water, with combined Uranium levels up to 6.8 ppb. (The EPA recommended limit is 0.50 ppb.)

CHEMICAL AND PHYSICAL DATA (Source: CT College, Connecticut Biotic Survey and Inventory, Year? http://fmp.conncoll.edu/Silicasecchidisk/Connecticut_Lakes_Frameset_New.html)

Alkalinity: 0.52 meq/L

Ca++ (Calcium): 0.39 meq/L

K+: 0.06 meq/L

Mg++ (manganese): 0.14 meq/L

NA+ (sodium): 0.23 meq/L

pH: 8.6

Secchi Disk: 0.9 meters. Note: Citizen volunteers have been conducting periodic Secchi Disk monitoring in 2013 and 2014 under the auspices of the ECCD.

  • Historical Secchi Disk Readings via Landsat Imagery:
  • 1974: 2.0 (05/02/1974)
  • 1974: 2.5 (07/17/1974)
  • 1974: 3.0 (08/01/1974)
  • 1992: 1.2 (06/11/1992)
  • 1993: 0.6 (06/28/1993)


Specific Conductivity: 104 uS/cm

Sulfate: 0.18 meq/L

Total Nitrogen: 1263 ug/L

Total Phosphorus: 96 ug/L. Even in the 1990's, phosphorus levels at Roseland Lake were extraordinarily high. (Source: Historical Changes in Connecticut Lakes Over a 55-Year Period)

Turbidity: The lake is turbid, with visibility of about 2 feet in late summer.

Dissolved Oxygen: dissolved oxygen levels in Roseland Lake