Since October 1999, the Iowa Department of Natural Resources has maintained a network of stations to monitor water quality in the state. A total of 91 sites have been part of this network. However, the total number of stations monitored varies each year. The most stations sampled was in 2003-2006 when a total of 84 stream sites and 1 spring were sampled. Currently, a total of 75 stream sites and 1 spring are sampled. Generally, the sites in this network are sampled monthly.