Man-made Lake Research Team

Advancements in technology, specifically Global Information Systems (GIS), have provided new tools and methods to measure sediment accumulation in Iowa lake basins. All of Iowa’s significant public owned lakes (SPOLs) were surveyed between 2006 and 2016 to measure lake depth at a known elevation or lake level. Contour maps, similar to topographic maps, were created and provided for several user groups working and recreating on Iowa lakes. Engineers, management biologists, and anglers are some of the users that request the available depth data found on the Iowa DNR website. The known elevation is a bench mark allowing multiple surveys to be compared over time to compare apples to apples and measure accumulated sediment in lake basins.

Surveys completed in 2012 can be compared with more recent surveys to calculate accumulated sediment in lake basins. Why is this important? Accumulated sediment can negatively affect water quality, change fish composition and size structure, and increase vegetation growth that have negative effects on recreational activities.

During the last five years, 35 lakes have been surveyed for a second time. The initial surveys were completed about 10 years ago. We found sediment accumulation in these lakes to be between .35 percent and .64 percent each year. This means a 100 acre lake with a volume of 700 ac-ft can gain between 430 and 650 dump truck loads of soil each year depending on the size of its watershed and land use types. The accuracy of these sediment accumulation values is between 4 percent and 6 percent based on our results from this study. After this study is finalized, we will evaluate models used to estimate accumulated sediments and help improve longevity of restoration projects and benefit anglers.

Iowa’s Community Fishing Program started in 2016 to increase angling participation and opportunities within Iowa’s larger cities. New initiatives in Iowa, such as the Community Fishing Program, aim to bridge the gap between natural resources and urban populations and increase angler participation. Over 200 ponds can be found in these populated areas ranging in size from 0.5 to 232 acres, all of which are located within 38 communities. Several ponds are added to this list each year as new developments are constructed. Managing all of these systems for fishing requires a different set of tools than traditional methods used for rural ponds.

During 2022, we collected trip information about anglers using urban ponds. Urban ponds were located in business parks, near schools, incorporated into parks with amenities, and part of neighborhoods. Preliminary analysis showed more fish were released than harvested, meaning people just wanted to catch fish to have a successful trip. The majority of angling in neighborhood ponds was by kids less than 16 years old. The average trip length was shorter in these community fisheries compared to rural ponds, urban lakes were between .7 and 1.1 hours. Many of these urban ponds are in backyards or only a short walk away from homes, therefore short trips would be expected. Angling effort can also be up to 10 times higher in urban ponds compared to rural locations. Urban ponds were similar to rural ponds regarding sport fish quality ranging from poor to excellent.

Even though sport fish population collections are similar between rural and urban locations, fish sampling gear types may need to be changed. Some pond basins in urban locations were built as water control structures and didn’t consider angler access. Next year the Small Impoundment research team will collect additional data and provide managers with the appropriate tools to provide urban anglers with quality experiences.

In a recent survey, 76 percent of Iowa anglers rated the Iowa DNR as excellent or good in managing fishing and fisheries in Iowa. Fisheries managers need up-to-date information on fish populations to maintain this high level of angler satisfaction.

In the early 2000’s, the Iowa DNR collected bluegill age and growth information statewide from Significant Public Owned Lakes (SPOLs). Since then, a statewide bluegill bag limit was established and numerous fisheries were renovated through the Iowa DNR’s Lake Restoration Program. Bluegill age-growth information was collected sporadically during this period, primarily for special projects; but, a similar statewide assessment has not been completed for almost 20 years. This information is needed to evaluate the many management actions during this period.

Bluegill populations were surveyed in 23 lakes in the fall between 2020 and 2022. Age structures were collected from approximately 1,725 fish between 3- and 10-inches. These fish were also weighed, measured for length, and sex was determined for mature individuals. Results show males grow slightly faster than females, and the maximum age collected to date for this study is 11 years with the majority reaching 8 years. Length-at-age data also suggested a difference in fish size from northern latitude to southern latitude, fish were larger in southern impoundments than northern climate impoundments.

Lakes sampled in the next two years will add to these results and assist management biologists in making science based decisions for managing bluegill in Iowa.

Bluegill are a popular sport fish in Iowa with 58 percent of anglers indicating they fished for bluegill in a 2019 survey. Bluegill are found in most Iowa impoundments and are usually part of the first stocking in new or renovated lakes and ponds. When the Iowa DNR restocks bluegill after a lake renovation, the goal is for 8-inch bluegill to be available to anglers within four years after restocking.

This goal is achieved in some cases when water quality is improved, but there are exceptions. When these exceptions occur and are not explainable, fisheries managers question if the broodstock source might be a contributing factor. Bluegill stocking rates have been reduced in recent years to keep the initial year-class following a renovation from getting overabundant before the first year-class of largemouth bass can be established. If this initial bluegill stocking is supplemented from another source (e.g., fish escaping from ponds in the watershed or illegal stockings), it may result in density dependent growth that prevents bluegill from achieving the desired growth rate. Some bluegill sources may have genetics that lend themselves to faster growth.

During the 2020, 2021 and 2022 sampling seasons, bluegill genetic samples were collected from fin clips.These fish were collected from multiple lakes representing five different bluegill populations and progeny from two fish hatcheries. Results showed bluegill populations were different between the three lakes. There is also evidence that certain genes may contribute to growth. Additional testing will be conducted to confirm these results.

Information from this study will be used to guide future bluegill restocking efforts following lake renovations. The ultimate goal for bluegill fisheries after renovation is to provide anglers with desirable-sized fish as soon as possible after a fishery renovation.

Walleye are a popular sport fish in Iowa, ranking in the top two most fished for species. Walleye can be caught in lakes, interior rivers, and large rivers. Walleye are stocked into lakes as fry, fingerling, and advanced fingerling sizes to maintain quality populations across the state in lakes and rivers. Advanced fingerling fish are the largest of the three sizes ranging between 6-inches and 12-inches long and cost more to raise than the other two sizes of fish. When these fish are stocked, it is important to see them survive and grow so anglers have an opportunity to catch them or they become part of the broodstock population in Iowa lakes.

New fish rearing methods have been developed with the nationwide spread of aquatic invasive species (AIS), such as zebra mussels. These invasive species can cause significant damage to native ecosystems and infrastructure. Fish hatcheries can combat AIS species by switching from a flow-through system to using a recirculating aquaculture system (RAS). This type of system uses clean water free of AIS species which reduces hatchery costs and problems associated with hauling fish to stock in lakes.

Rathbun Fish Hatchery, located in Southern Iowa, can raise walleye in a RAS from egg to advanced fingerling size and avoid AIS problems, but these fish have not been evaluated after stocking into a lake to see if their survival is similar to advanced fingerling walleye raised in a traditional flow-through system. In 2021, walleye were implanted with radio tags to monitor survival over 8 months. Results showed walleye reared in a RAS had similar survival rates to walleye reared in a flow-through system. This radio telemetry project also showed RAS fish moved greater distances between tracking events. 

In 2019, 2020, and 2021 three different advanced fingerling walleye products were stocked into lakes in October and then sampled in 2020, 2021, and 2022 to evaluate how each product survived after stocking. Sampling results in 2020 and 2021 for age-1 fish were dominated with fish grown in a flow-through system. Walleye reared in a RAS and collected in 2022 at age-1 were sampled at a significantly higher number than in 2020 and 2021. Sampling results for age-2 Walleye were dominated by fish grown in a flow-through system and RAS fish were sampled in low numbers. These results suggest a quality RAS product can survive in lakes and more work is still needed to improve our understanding about the contribution of RAS reared Walleyes in Iowa lakes.

• Evaluation of Iowa's Standard Fisheries Sampling Programs: Electrofishing
• Evaluation of channel catfish populations in Iowa’s small constructed lakes
• Aquatic Plant Best Management Practices for Iowa's Public Lakes
• Pond Plant Identification Guide
• Evaluation of the Split Stocking Method in Iowa Ponds
• Evaluation of the Impact of Common Carp on an Intensively Managed Largemouth Bass, Channel Catfish, and Panfish Fishery
• Hydroacoustic Assessment of Iowa Lakes
• Developing Statewide Consumption Guidelines for Iowa Sport Fish