For the past three decades, municipalities in the United States have successfully addressed pollution in the watershed by collecting and treating their wastewater. Currently, all municipalities provide secondary level treatment, and in some cases tertiary treatment, and industries provide best available/best practicable treatment. This has had great benefits. More rivers are meeting water quality standards, and the public health is being protected from waterborne disease. The challenge now facing us is to address pollution associated with storm water runoff, since this is now the last major threat to water quality. It is less costly to prevent the generation of polluted runoff than to treat it. Today, many municipalities are implementing low-cost best management practices (BMPs) that prevent runoff. The lowest cost BMPs, termed non-structural or source control BMPs, include practices such as limiting pesticide use in agricultural areas or retaining rainwater on residential lots. There are a set of higher cost BMPs, which involve building a structure of some kind to store stormwater until it can be discharged into a nearby receiving water. These can be more costly, especially in areas where land costs are high. The three most commonly used structural treatment BMPs that will be discussed in the document are ponds (detention/retention), vegetated biofilters (swales and filter/buffer strips) and constructed wetlands. Two categories of treatment considered in this document are ponds and vegetated biofilters.