A benthic macroinvertebrate monitoring program known as the TREND program was created in the early 1970's and was based on the Baseline monitoring program established by the Interstate Commission Potomac River Basin (ICPRB) for the Potomac River. The program monitored the aquatic environment by sampling the community of macroinvertebrates at selected sites across Maryland. In response to the 1972 Federal Clean Water Act additional benthic macroinvertebrate sites (CORE) were added to the program and the CORE/TREND monitoring program was established in the early to mid 1970s. The overall plan and design of this program was to establish ambient water monitoring stations at fixed locations to document the status and determine long-term trends in water quality (QAQC 1995). These programs were intended to determine trends in water uses, impacts in problem areas, land use areas, and trends in areas where future development may influence water quality (U.S. EPA Report No. 440 1976). Stations were located, whenever possible, where historical data were available and within major rivers and larger tributaries of Maryland's drainage basins.