Greengots Lake in this example is based on a real 48,000 square meter lake in a temperate region of the United State. The shallow lake is a human-made lake with an average depth of 1m, and it was built to operate a grist mill. The lake water is no longer used for the mill, but is now a source for drinking water and recreational fishing. The source of water to the lake are a cold-water spring and the severely impaired Cooks Creek.

Cold water spring characteristics: Flow rate =10,600 m³/day; Dissolved Oxygen = 4mg/L; Phosphorous = 209 Kg/year; Temperature = 15 C.

Cooks Creek water characteristics: Flow rate =161,000 m³/day; Dissolved Oxygen = 3mg/L; Phosphorous = 4,250 Kg/year; Temperature = 23 C.

Other Phosphorous Loads: Row Crops from surrounding farmland = 7,410 Kg/year; Pasture/Hay = 700 Kg/yr; Undeveloped areas = 227 Kg/year; Urban Drainage = 1,020 Kg/yr; Septic Drainage = 200 Kg/yr

Calculate Outflow from the lake; hydraulic residence time in the lake, and steady-state phosphorus concentration in the lake.