Cladaphora, 2006 Water Quality Report to Congress

For the past five years, large quantities of decaying algae have been fouling Wisconsin´s Lake Michigan shoreline. As the algae and organisms trapped in the alga rot, they generate a pungent septic odor that many people confuse with sewage. Nutrient (phosphorus) sources, zebra and quagga mussels, declining lake levels, and changing lake currents have been implicated in the recent increase in nuisance algae. The presence of rotting Cladophora on Lake Michigan beaches presents aesthetic and odor problems that impairs recreational use of Lake Michigan. This algae, a green algae, does not present a risk to human health (unlike blue-green algae that can produce toxins). However, the rotting algae may provide adequate conditions for bacterial growth and crustaceans deposited on the beach with the decaying Cladophora may attract large flocks of gulls resulting in increased bacteria concentrations from gull fecal material.

Decaying algae smother a Wisconsin Great Lakes Beach.

Cladophora is a green algae found naturally along the Great Lakes coastlines. It grows on submerged rocks, logs or other hard surfaces. Because of Lake Michigan´s water clarity it has been observed growing at well over 30 feet of water depth. Wind and wave action cause the algae to break free from the lake bottom and wash up on shore. Nuisance levels of Cladophora were also a problem in the 1960´s and 1970´s. Research linked these blooms to high phosphorus levels in the water, mainly as a result of human activities such as fertilizing lawns, poorly maintained septic systems, inadequate sewage treatment, agricultural runoff and detergents containing phosphorus. Due to tighter restrictions, phosphorus levels declined during the 1970´s and Cladophora blooms were largely absent in the 1980´s and 90´s. Phosphorus levels in Lake Michigan continue to remain below the thresholds set in the 1970´s, but recent research suggests that the invasion of zebra and quagga mussels in the Great Lakes are responsible for the increase in algae by increasing the availability of phosphorus for Cladophora in the nearshore zone and increasing water clarity.

Researchers investigate algae problems.

In 2004 the Wisconsin DNR began an algae, zebra mussel, and nearshore nutrient monitoring program in Lake Michigan to understand the distribution and extent of the Cladophora problem. The Wisconsin DNR is currently working in collaboration with the UWM Cladophora research program to assist in data collection for the development of a Lake Michigan Cladophora growth model that will assist with management efforts. In addition the WDNR is developing guidance and a general permit for Cladophora removal and beach management activities. Because we can not control zebra and quagga mussel populations our only long term management option available is to reduce phosphorus entering Lake Michigan. Reducing stormwater runoff, agricultural runoff and maintaining septic systems are all important to reducing phosphorus loads to Lake Michigan.