Hampshire, the Farmington River in Connecticut, and the Neversink River in New York harbor large populations, but these number in the thousands only. The remaining populations from New Jersey south to North Carolina are estimated at a few individuals to a few hundred individuals. Strayer et al. (1996) speculated that many dwarf wedgemussel populations, particularly in the southern portion of the range, may be threatened by low densities, small ranges. and linear structure (i.e., an entire population in one stream with no possibility of refuge from catastrophes or stochastic events). Low-density populations may lead to a loss of productivity due to reproductive impediments (e.g., the distance between mussels being too great) or loss of genetic variability. The Mill River in Hatfield and Whately, Massachusetts is an example of a river with a dwarf wedgemussel population patchily distributed over an approximate 16-mile stretch. The most reproductively robust patch is limited to a small stretch (< 1 mile) making it extremely vulnerable to a catastrophic event. The remainder dwarf wedgemussels are sparsely scattered and may demonstrate a reduced capability to reproduce as indicated by McLain and Ross (2005). Agricultural run-off has been identified as a significant threat to dwarf wedgemussel populations in Massachusetts, Maryland, and North Carolina. In 2001, more than 25 dwarf wedgemussels and hundreds of other mussels (including state-listed species) were killed in the Mill River, Massachusetts, by waste run-off from a small farm. Recently, severe flooding in the Baltimore and Neversink Rivers in Pennsylvania and New York, respectively, resulted in the destruction of occupied habitat and loss of dwarf wedgemussels. Surveys conducted at two sites on the Neversink River below a dam in Cuddebackville, New York, derived abundance estimates ranging from 60 to 500 dwarf wedgemussels per site (Cole et al. 2004) prior to 2005. Severe flooding in the spring of 2005 scoured the river channel and deposited cobble in at least one of the sites previously surveyed. Resurveys in 2005 of the two sites conducted after the flood event detected one fresh dead dwarf wedgemussel and no live mussels (Cole and White 2006). Surveys in 2006 indicated that the dwarf wedgemussel population in the Neversink River was adversely affected by flood events, although some live mussels were detected. Little riverine habitat adjacent to extant populations is protected other than by state shoreline protection regulations or local land use regulations. Development of adjacent uplands continues to be a significant