Minnesota removed common carp; lake clarity rose nearly 600% afterward

For decades, Pickerel Lake in Minnesota struggled with poor water quality, heavy algal growth and extremely low aquatic plant cover. The shallow lake had become dominated by common carp, a bottom-feeding fish that can disturb lake sediments and alter the movement of nutrients through an aquatic ecosystem.But after the invasive fish were removed in 2009, the lake underwent a dramatic ecological transformation. Water became substantially clearer, phosphorus levels fell, algae declined and aquatic plants returned across much of the lake. A study published in Inland Waters found that removing common carp was followed by major improvements in both water quality and the lake’s biological community.Pickerel Lake, located near Albert Lea in southern Minnesota, covers about 281 hectares and is extremely shallow, with an average depth of only 1.2 metres and a maximum depth of 1.8 metres. Records of degraded water quality date back to at least 1948, when the lake was described as having poor water clarity and heavy algal blooms.Common carp had become a major problem. The fish are native to Eastern Europe and Asia but have been introduced widely around the world and are considered among the mo...