Runoff
Polluted stormwater runoff is the largest factor affecting water quality in the Monona Bay watershed. Impermeable surfaces such as roads, parking lots and buildings prevent rain water from filtering through the soil into the groundwater. Instead, rain water carries pollutants to our lakes.

Pollution
Storm water outflows transport a variety of pollutants into the Bay. Rain and melting snow flow into storm drains, carrying with them trash, soil particles, bacteria, pesticides, fertilizer, pet wastes, road salt and sand, oil, and other toxic materials. This polluted runoff is the number one cause of water quality problems in Monona Bay, as well as almost all other lakes in Wisconsin.

Lake weeds and algae
The abundance of lake weeds and algae during summer months is the result of decades of polluted runoff. Lake weeds are "fed" by nutrients in bottom sediments, while phosphorus contributing to nuisance algae blooms comes from runoff. Phosphorus from leaves, grass, yard clippings and chemical fertilizers enters our waters via runoff and sediment. Phosphorus is often attached to the sediment that gets washed into storm drains. The amount of sediment and debris washing into the Bay is especially visible at the outflow near Parr Street when water levels are low.

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