Mirror Lake and Swan Lake in Storrs, CT are man-made ponds serving as central landscape elements on the University of Connecticut's main campus. The University of Connecticut campus is an island city amid suburban and agricultural land uses. Peak campus population is approx. 20,000 persons. More important is the University's ten-year program of infrastructure improvement to upgrade the campus and add new buildings. Water quality in Mirror and Swan Lakes became (very) poor due to the large area of impervious surface and to yearly influxes of road-sand and salt, lawn fertilizers, traffic-related pollutants, and sediment from erosion and construction on campus. As well, by the 1970's a flock of geese occasionally numbering as many as 1,000 birds became permanent. These geese feed regularly on the surrounding lawns and contribute nutrient-laden feces to the Ponds. The external nutrient loading from the drainage basins, direct input of feces by waterfowl as well as internal nutrient loading from the sediments, has contributed to continuing periodic summer anoxia in Mirror Lake. There have been die-offs of the geese and ducks due to Clostridium bacilli (botulism) poisoning from bottom sediments. Concentrations as high as 450µg-P/L cause severe loading to exit streams (Willow Brook) and receiving waters (~1 mile distant), the Fenton River. Periodically, attached algae grow on the bottom of Willow Brook to its confluence with the Fenton River and for some distance downstream in the Fenton. (The Fenton River is treated as a Class A steam by the CT Dept of Environmental Protection and is under consideration to receive a permanent breeding population of trout.) Attached algae are likely associated with high phosphorus in water leaving and immediately downstream of Mirror Lake. Given the very public location of these ponds, and proximity to a large population of students and waterfowl, they constitute an attractive nuisance and potential environmental issue.

Physical Characteristics

Some of the key physical characteristics of the ponds are listed in the table above. In addition, a Microsoft Excel file containing this information as well as volume and area as a function of depth can be downloaded by clicking here and downloading the file Pond_Bathymetry.xls.

The ponds receive their inflow from surface runoff as well as piped storm drainage. Mirror Lake has one outflow that drains over a spillway to Willow Brook and eventually to the Fenton River. Swan Lake has two outlets, one under the chemistry building towards the west campus and eventually into a small brook, and another outflow into a drainage pipe under the road and into Willow Brook. Only under extreme flow events does water flow out of Swan Lake towards the west. Most often outflow is from Swan Lake towards Willow Brook, but there may also be leakage into the ground and/or into the storm drain at locations that cannot be gauged. For this reason, Swan Lake residence times are best inferred from the volume and the inflow.

Swan Lake has benthic pumps installed that results in high oxygen water but a proliferation of green macroalgae that reduces the aesthetic appeal of the pond. This system was installed under the misconception that bottom water was low in oxygen and required aeration. However, the pump moves deep nutrient rich water to the surface and surface water to depth resulting in high nutrient loads at the surface and hence the proliferation of macroalgae. The University has since been convinced to turn the benthic pump OFF although it may be the centerpiece of future experiments.