Urban areas have the potential to pollute water in many ways. Runoff from streets carries oil, rubber, heavy metals, and other contaminants from automobiles. Untreated or poorly treated sewage can be low in dissolved oxygen and high in pollutants such as fecal coliform bacteria, nitrates, phosphorus, chemicals, and other bacteria. Treated sewage can still be high in nitrates. Groundwater and surface water can be contaminated from many sources such as garbage dumps, toxic waste and chemical storage and use areas, leaking fuel storage tanks, and intentional dumping of hazardous substances. Air pollution can lead to acid rain, nitrate deposition, and ammonium deposition, which can alter the water chemistry of lakes.

Solutions

Solutions involve finding sustainable ways for the urban area to reduce both its dependence on pollutants and the amount of pollutants it produces, and to properly recycle or dispose of pollutants before they contaminate soil, water, or air. See the discussion below under "Lakes that Face this Problem" for more detailed solutions that have been tried at various lakes.

Preventing pollution in urban areas is often largely a public relations task. People need to be educated about proper ways to dispose of waste. Showing each other where waste goes and the problems it can create in our watersheds is an effective way to get the message across.

Of course, regulations are often necessary to reduce the amount of pollutants contaminating our watersheds, and the Lake Biwa Ordinance is an example of regulatory measures (such as prohibiting synthetic detergents) making a big difference.

Lakes that face this problem

The Broads, United Kingdom
Phosphate-rich sewage effluent from the growing human population in the Broads has gradually entered the Broads waterways. This led to the growth of algae, loss of water plants and a serious decline in the wildlife interest of the broads. Phosphate stripping and suction dredging are being used to address this problem.

La Nava Wetland, Spain
(FPNE) is working to solve pollution problems affecting La Nava Wetland. Solutions include purifying wastewater draining into the wetland, rerouting drainage ditches, and closing a garbage dump that releases contaminants.

Lake Biwa, Japan
Since the 1970s, nutrient pollution from nitrogen and phosphorus runoff has caused algae blooms and eutrophication. The government has set pollution reduction goals and banned the destruction of reed marshes.