Lake Francis Case Walleye Population Continues Positive Trend

The Lake Francis Case walleye population has been a subject of discussion in recent years, as anglers have reported a bit tougher fishing on the reservoir. The toughest bite was in 2024, and the 2025 season showed signs of improvement. Heading into 2026, these signs continue to point towards an upswing in the walleye fishing on the 107-mile-long reservoir.

Lake Francis Case sits below Big Bend Dam in Fort Thompson, and above Fort Randall Dam in Pickstown. It is the 11th largest reservoir in the United States, spanning 102,000 acres with a max depth of 140 feet. South Dakota Game, Fish and Parks (GFP) fisheries biologists annually place 75 gill nets across the reservoir in September, and shared the results of these surveys at a public virtual meeting February 17, 2026. 

Walleye were the most prominent catch in these nets, consisting of 31% of the total catch. Sauger added an additional 9%, bringing the combination of walleye and sauger to 40% of the fish sampled. Channel catfish were behind with 20% of the catch, smallmouth bass were 8%, and notably gizzard shad were 2%. 

The Lake Francis Case walleye abundance can be correlated to runoff, although not at the level seen on Lewis and Clark Lake as Lake Francis Case is a larger waterbody. Decreased runoff results in decreased nutrient inflow, while increased runoff results in higher nutrient inflow. Generally speaking the higher the nutrient inflow, the higher the walleye abundance. 

The 2025 walleye abundance in Lake Francis Case is higher than it was in 2023 and 2024, and on par with the average from 2017-2022, which is about five walleye per net. The best way to evaluate the population is by trends as opposed to individual years, and currently the walleye population appears to be trending upwards and near average.

Lake Francis Case has a 15 inch minimum length limit for walleye, and sampling results show there are plenty of harvestable fish to be caught. Approximately 45% of the walleye in gill net catches were over 15 inches and of these about 10% were above 20 inches. In addition to these, there are good year classes of fish coming up to take their place.

These fish are also in very good condition. Fisheries biologists measure fish relative plumpness, or Wr, with average being a value around 80. Lake Francis Case consistently exceeds this range, usually between 80-90. 

Prey abundance has a major role in this, and a good example of this would be the 2024 season, which saw significant over winter survival of shad. This resulted in an abundance of prey beginning in spring, and continuing throughout the season, resulting in fat and happy fish that were exceeding a Wr of 90.

In 2025, Wr returned closer to average, coming in at 85. 

A second key metric of growth is walleye length at age-3. In general, fisheries biologists want to see fish approximately 15 inches at age-3. Lake Francis Case fish grow fast and often exceed this 15-inch benchmark.

In 2025, age-3 walleye were right at average with a length of 16 ½ inches. By age-5, these fish were at 18 inches. These are all very good indicators that Lake Francis Case walleye are growing well.

As far as age structure within the fishery, there is a big number of age 1, 2, and 3 walleyes. This can be expected, as these are all fish that are below, or just reaching, the 15-inch minimum.

There is also a larger number of age-6 fish, which would have been produced as a large year class in 2019, a period that correlated with high flows into the system. These fish are larger, coming in around 18 ½ inches.

Gill net surveys take place in September, and provide a snapshot of the fishery. At the time of sampling, the best net catches were mainly from the Boyer to Whetstone Bay area, which is primarily the central part of the reservoir. While fish were caught throughout the entire reservoir, at this time, the upper end of the reservoir had the fewest fish.

In addition to gill net surveys, electrofishing is conducted to determine age-0 walleye abundance. The average walleye per hour is 150 fish, which is a very high number. For comparison, Lewis and Clark Lake walleye per hour averages near 44, and the strong years of recent come in approximately 100 walleye per hour.

In 2025 electrofishing catch rate was a big lower at around 55 walleyes per hour. While this is a lower than average number for Lake Francis Case, it continues a trend of the fishery consistently producing a year class each season. Following average to above average production in recent years, year class suppression can also occur, which could be a factor in 2025.

In all, the Lake Francis Case walleye population continues an upswing that has been taking place since lower years in 2023 and 2024. There is a strong number of fish over 15 inches, which can be harvested by anglers, as well as fish greater than 20 inches to be caught too.

Anglers can expect to see an increased number of 18-19 inch walleye, courtesy of a strong year class in 2019, and there are plenty of fish between 15-17 inches, as well as those “unders”, to be caught as well. 

These walleyes are in very good shape, eating well and growing quickly, with conditions continuing to be above average. Runoff, gizzard shad survival and abundance, and year-class sizes will all continue to impact the fishery on a year to year basis, but overall the walleye factory that is Lake Francis Case continues to produce. 

Learn More About Walleye Fishing on Lake Francis Case

Anglers looking to learn more about walleye fishing throughout the season, including locations and techniques, can find everything they need to know and more in The Complete Guide to Fishing on Lake Francis Case. Whether it’s spring walleye fishing or the middle of summer, this guide breaks down everything there is to know about targeting walleye on Lake Francis Case.