Like many American rivers, the Winooski has been used to dispose of many different types of waste over the years, including sewage and discharge from mills. In fact, as recently as 1968, much of the Winooski' s water was rated class D the lowest water classification with high levels of bacteria, floating solids and human waste.
Since the early 1970s, the Winooski River' s water quality has improved immensely, and as a result all sections of the river are now classified as either B or C. Class B water is suitable for public water supply with filtration and disinfection; irrigation and other agricultural uses; swimming and recreation. About 40 percent of the river is suitable for swimming. Class C water is suitable for recreational boating and any recreational or other water uses where contact with water is minimal and ingestion of the water is not probable; irrigation of crops not used for human consumption without cooking; and compatible industrial uses.
Today, two of the greatest threats to river water quality are non-point source pollution and treated wastewater pollution from both municipal and industrial sources. There are a number of municipal and one private sewage treatment facilities on the Winooski and its tributaries. On the main river, locations include: Marshfield, Plainfield, Waterbury, Richmond, Essex Junction, Burlington (Riverside), Winooski, Burlington (North End), and IBM. Wastewater from these plants adds nutrients to the water. Many of these substances contain nitrogen and phosphorous which make aquatic plants, such as algae, grow quickly. The decay of these plants and the presence of organic material in waste water depletes oxygen out of the water, which in turn can cause problems for the river' s fisheries.
In addition to sewage and industrial discharge, other forms of water pollution threaten the Winooski, as they do most rivers throughout the United States. Although there is little information about the precise source or content of much urban runoff in Vermont, it can contain heavy metals and other contaminants. Runoff along the Winooski has been found to include oil, grease and road salts washing into the river from adjacent streets and highways. Also, with the growth and development of towns along the river, trees and shrubs are cut down, which allows more soil erosion to occur along the banks. The result is increased sediment in the river which can hurt clear water fish species such as trout and salmon.
Agriculture has always played an important role along the Winooski. Unlike agricultural runoff in the 18th century, today's runoff can contain traces of pesticides and herbicides. Fertilizers and manure contain nutrients that have the same effects as those discharged from the treatment plants.
There have been efforts to clean up the river. Sand has replaced salt on most bridges in the winters, and Vermont has increased Soil Conservation Service projects that involve the voluntary participation of farmers to improve manure disposal practices and reduce agricultural nonpoint pollution. In addition, several private organizations routinely monitor the river' s quality, and the government has placed strict standards on sewage treatment and industrial discharge. In recent years, due to increased efforts by government, business, farmers and citizens, the Winooski' s wildlife and fish have begun to make a comeback--a sign of a clean, healthy river.