Water Quality Trends for Minnesota Rivers and Streams at Milestone Sites

Long-term trend analysis of seven different water pollutants measured at 80 locations across Minnesota for more than 30 years shows consistent reductions in five pollutants, but consistent increases in two pollutants. Concentrations of total suspended solids, phosphorus, ammonia, biochemical oxygen demand, and bacteria have significantly decreased, but nitrate and chloride concentrations have risen, according to data from the Minnesota Pollution Control Agency's (MPCA) "Milestone" monitoring network. Recent, shorter-term trends are consistent with this pattern, but are less pronounced. Pollutant concentrations show distinct regional differences, with a general pattern across the state of lower levels in the northeast to higher levels in the southwest. These trends reflect both the successes of cleaning up municipal and industrial pollutant discharges during this period, and the continuing challenge of controlling the more diffuse "nonpoint" polluted runoff sources and the impacts of increased water volumes from artificial drainage practices.