News : What's in the Watershed?

By Camryn Grubic

It shouldn't come as a shock to anyone who knows a thing or two about conservation that Iowa's waterways and aquatic ecosystems are under threat. Let me share with you some of the steps Benton County Conservation has been taking to secure a safer and healthier future for one of our designated hotspots, Hannen Lake Park.

Hannen Lake Park was the first county conservation manmade lake in the State of Iowa, and was completed in 1958. Several basin cleanouts, sediment mitigation tasks, and shoreline infrastructure projects have been completed by the county with the help of partnering agencies over the last 67 years. The current conservation board and staff want to take even bigger steps to ensure that the next several decades of recreation and service at our lakes can provide the healthiest experiences for you.

Though Hannen Lake has been listed as an "impaired waterway" by the Iowa Department of Natural Resources for over a decade, it doesn't mean that it is unsafe to swim or fish out of. BCCB participates in an annual lake monitoring study, tracking swimming safety standards from Memorial Day through Labor Day each year. Those results are published online, and warnings are posted at swimming locations if necessary. However, we almost never have increased levels of bacteria per the state lab's standards, but always feel free to reach out and ask. The IDNR states Hannen Lake is impaired due to algal growth and increased turbidity, which simply means "water that has become cloudy or murky due to the presence of suspended solids like silt, mud, algae, or other particles".

What's in the Watershed?

What is causing this turbidity? What is really in the watershed? The answer is sediment caused by erosion! Hannen Lake's watershed (approximately 603 acres), or the area of acreage that drains into the lake in the event of rainfall, is experiencing harsh erosion conditions. If you have taken the time to enjoy a hike along any of the trails at the park, it is easy to notice the excess gulley erosion where two hills converge at their bases. In some areas it looks like a miniature gorge where rain settles into the base between two large hills, creating a stream which churns up mud along the way, before finally draining into the lake.

Can we stop it? Yes, we can! Conservation staff at Benton County have been working to develop a coordinated effort between our department and the Iowa DNR lake restoration team, and a plan is in the works. Lake monitoring and lab work is being conducted through 2025 to better understand the chemistry and ecology of Hannen Lake, and it was remapped in 2024 to compare sediment levels to the previous bathymetry map from 2012. This is a slow process, but worth the wait for good comparable data. In the meantime, our conservation staff has identified areas of concern and has begun tackling some of those with boots and equipment on the ground. A significant portion of that is the much-needed cleanup of crowded pine plantings that took the front of the 2020 derecho, which will now be converted to tallgrass prairie in an effort to enhance water quality and habitat abundance. Our naturalists will tell you that one acre of prairie will absorb 9 inches of rain per acre per hour, a statistic from UNI's Tallgrass Prairie Center. That is a lot! We've already converted 12 acres of excess mowed grass hill slopes to prairie in 2023, and plan to establish tallgrass prairie in another 20+ acres of park area in the near future. This will help to ensure the water that does inevitably make it into the lake is as clean and free of soil and other nutrient particles as possible.

The time is now, and at Benton County Conservation, we realize that. We want to make sure that the steps we are taking today will ensure another 67+ years of Hannen Lake so that it doesn't become "Hannen Shallow Wetland". But it all takes time, and we hope that you know that. Trust me, we are on the move! One of the best perks of the job is to hear of the family memories, traditions, and ever-changing landscapes at our parks, and we will continue to keep those best interests in mind. Here's to many more years to come at Hannen Lake Park!