Indian River and Rehoboth Bays both suffer from varying degrees of eutrophication. Such nutrient over-enrichment results in undesirable phytoplankton and macroalgae blooms, both of which lead to declines in dissolved oxygen levels and light penetration. Such effects have been considered major contributors to the disappearance of SVP in Delaware, and to declines in desirable finfish and shellfish populations. Extensive declines in SVP populations have been documented along the East Coast since the 1930s, and attributed primarily to increased turbidity of the water column due to excessive nutrient and sediment loading. Sources of increased nutrients include non-point sources such as agricultural runoff and domestic septic systems, and point sources such as sewage and storm water discharge.
Sediment loading comes from both rural and urban runoff as well as shoreline erosion.
Specifically, water quality within all of Delmarva's coastal bays has significantly deteriorated since the 1960's. As a result, SVP have disappeared from many of these embayments. A 1998 study suggested that areas within Delaware's coastal bays that historically supported SVP, and areas that meet the minimum requirements set forth by the Chesapeake Bay Program's habitat parameters could be potential SVP restoration sites. Plants overcame transplant trauma, and successfully overwintered, but were uprooted by recreational clammers in June of 1991. During the fall of 1991, Z. marina seeds were broadcast in three areas of Rehoboth and Indian River Bays.