Restoration Efforts Undertaken on the County K Marsh

The GLSD and Lake Management Team Partners have been working for years to improve the water quality entering the lake from the County K marsh. The marsh contributes a disproportionate amount of nutrients to Green Lake than is accounted for by the size of its 3 subwatersheds (Wurches Creek, Spring Creek, and Roy Creek). This has long been a concern to our lake managers. The highly turbid water and lack of aquatic plants indicate the marsh is not functioning as it should. We know that to reduce the phosphorus in Big Green Lake, we need to address nutrient loading into and nutrient cycling within the K marsh.

There are many variables involved with the nutrient cycling in the marsh. Carp can cause major impacts to shallow-water areas by stirring sediment and creating unstable shoreline areas. The GLSD and DNR installed and operate a carp barrier at the County K bridge which limits carp access into the marsh. Additionally, the GLSD and GLA have funded a carp harvesting program in the marsh for the past several years. We feel these efforts are beginning to show results based on the smaller size and limited numbers of carp harvested from the marsh in 2019.

Erosion from streambank and upland areas around the marsh have also contributed to sediment loading into the system. The GLSD has been working hard with our partners to fund streambank stabilization projects as well as agricultural BMPs to limit soil loss into the marsh. Another interesting factor impacting the marsh’s health is the shape and layout of the marsh itself. It is a shallow system; depths average 3 to 4 feet. The southwest-northeast orientation of the marsh allows for prevailing winds from the southwest (as well as the seemingly more frequent northeast wind events) to create strong wave action which, in conjunction with the carp, are causing increased shoreline erosion and destabilization of the phosphorus-rich marsh sediments. All these factors together keep the water in the marsh too turbid for aquatic plants to grow. The root systems of these plants would, in turn, help stabilize the sediments.

To this end, the GLSD, with funding from the DNR and with the support of our partners, coordinated a restoration project in the marsh that involved reducing both wave energy and carp impacts in several bays. It took weeks of planning, obtaining permits, coordinating materials and boats, retrofitting barrier sections, processing the plant material, etc. – but the turbidity barrier and accompanying plant material was installed at the end of May. 

To accomplish this project, floating turbidity barriers were installed across the entrances to the bays. The barriers break up the distance waves have to gain energy before hitting the shoreline. Additionally, the barriers limit carp access since they reach from the firm marsh bottom to the water surface. Inside these enclosures we restored native submergent and emergent plant species such as wild rice and sago pondweed. We are hoping to also see some natural regeneration of plants that may have previously been limited by the water’s turbidity. As with the carp removal, this project is a multiyear effort. After 1 to 3 years, the barriers will be moved to new locations within the marsh as aquatic plants become established in each area.

The project was coordinated and installed almost entirely by GLSD staff. We’re proud of all the effort undertaken to make this happen – especially as the Covid-19 lockdown made all aspects even more challenging.