By: Bill Boettge
For some it is the thrill of watching your bobber go underwater and the anticipation of a nice sized bluegill or perch on the end of the line. For others, especially young granddaughters, it is the excitement of a fast ride on a tube with water spraying on her face. For everyone, it is a beautiful sunset on a warm summer evening. Beaver Dam Lake offers the residents of the area many great benefits.
Beaver Dam Lake was formed when the first settlers dammed up the river in 1846. I wonder if they realized that they would be creating the 16th largest lake in Wisconsin? While the river is not large, it collects water from 154 square miles of watershed, an area covering parts of four counties. There are 13 acres of watershed for every acre of lake.
While we knew the basic facts about the lake, and other reports have been written, there has been no comprehensive study of the lake. To better understand the lake’s ecosystem and the actions that can be taken to enhance and protect it, the Beaver Dam Lake Improvement Association (BDLIA) began a lake management study in 2012 using funds from a matching Wisconsin Department of Natural Resources (WDNR) grant. In addition to studying the water quality and drivers affecting water quality, the study provides detailed information on the aquatic plants, shore land assessment and fisheries data. From this, an implementation plan was developed through the collaborative efforts of the BDLIA, the ecologists doing the research and the WDNR. This plan was presented to the BDLIA members and interested citizens on August 22 at the BDLIA annual meeting. While the plan details specific goals and action items, it is a living document that will be under constant review and adjustment depending on conditions of the lake, the availability of funds, the level of volunteer involvement and the needs of the stakeholders.
Beaver Dam Lake is a “drainage” lake dependent primarily on runoff from the watershed for its source of water as opposed to being filled with water from springs. The lake serves as a collection basin for what flows from the watershed. Because this watershed is over 70% agricultural, we collect the soil (sediment) and the nutrients running off of this farmland. Over the past 175 plus years, the lake has been filled in with this sediment and collected the phosphorus and other nutrients. Thus it came as no surprise when the study found that we had ten times the phosphorus concentration of other shallow drainage lakes in Wisconsin. This high concentration of phosphorus results in the growth of algae, which in turn gives us poor water clarity, three to four times lower than other shallow drainage lakes in Wisconsin.
While the lake still collects over 46,000 pounds of phosphorus each year from runoff into the lake, the major source of phosphorus in our lake at this time is from the resuspension of the phosphorus already on the lake bottom and our large carp population. In shallow lakes, wind-induced sediment resuspension leads to increased total phosphorus concentrations and total suspended solids. Common carp directly increase nutrients within the water through foraging and spawning behavior, as well as through excretion. Studies have shown that one pound of carp in a lake produces 0.11 pounds of phosphorus through excretion and resuspension of bottom sediments. Based on the carp population in Beaver Dam Lake, they produce approximately 256,000 pounds of phosphorus per year. This is certainly a significant source of our phosphorus load and was one of the more important findings of the study. The implementation plan has several action items addressing this issue including the continuation of commercial harvesting of common carp from the lake. The goal is to harvest 40-60% of the carp population annually. In addition, the building of carp barriers to restrict carp from three major bays on the lake will not only help in limiting carp population but will enhance the aquatic plant community in these bays, which in turn will help the lakes fisheries.
The challenge to reduce wind-induced sediment resuspension is more difficult and very costly. However, the plan suggests we study the construction of wind barriers in the lake possibly through the dredging of specific areas of the lake to create these barriers. The side benefits of dredging would also improve navigation in certain areas of the lake.
To obtain a more accurate estimate of the amount of phosphorus originating from external and internal sources, an in-depth tributary monitoring study is in the implementation plan. The goal of this study would be to gain a more accurate estimate of the phosphorus being loaded in the lake via the watershed and from which sections of the watershed. This would also assist in our collaboration with the county land conservation departments as to how BDLIA can participate and assist with implementation of best management practices in the lake’s watershed.
This past spring, Beaver Dam Lake had an overabundance of curly-leaf pondweed, which is a non-native and invasive plant species. To manage this and to develop a plan to improve our aquatic plants in the lake, the BDLIA will seek a WDNR grant for 2016 to fund an invasive species assessment and develop an invasive species management strategy.
The fisheries are an important part of Beaver Dam Lake and included in the implementation plan to enhance the fishery on the lake are plans to expand course woody habitat as well as restore and preserve natural shore land through educational programs and use of the grants from the Healthy Lakes Initiative.
The Beaver Dam Lake Management Plan of 2015 is truly a very comprehensive document that addresses the issues and charts a course to improve our lake. The complete Beaver Dam Lake Management Plan is available online at www.BDLIA.org and is attached to this article. BDLIA welcomes your input and help. Email at email@example.com or call 920-356-1200.