The streams of the Severn watershed have suffered to varying degrees from the stresses of development, caused by the increased imperviousness of pavement and roofs. Rainwater that would have percolated through soil to recharge groundwater reservoirs becomes surface runoff, flowing directly to streams and resulting in excessive peak flows after storms. The resulting erosion degrades streambanks, loading the water with silt and nutrients. The natural cleansing mechanisms provided by the soil and its organisms are circumvented when runoff flows into streams, and the increased temperatures of runoff drive off dissolved oxygen in the water.
Streams of the Severn watershed that drain older developed areas tend to be the most impacted, since the importance of adequate stormwater treatment accompanying development has become recognized relatively recently. In 2001 a new set of more stringent stormwater management guidelines developed by the Maryland Department of the Environment becomes law in Anne Arundel County, and future development in the Severn watershed will have considerably less negative impact on the streams and the tidal Severn. In order to assess the health of the Severn's streams and prioritize retrofitting projects to provide enhanced stormwater controls for currently developed areas, Anne Arundel County has commissioned the Severn River Watershed Management Master Plan. This comprehensive study of watershed health and stormwater issues is currently underway, with considerable involvement of the Severn River Commission.