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. However, some sites in certain years have received more frequent monitoring to assess the impacts of flooding on the water quality. Each marker on the map represents one of the 91 monitoring sites. When a marker is clicked, a small window appears revealing detailed information about the site.