The walleye on the lower end of Lake Oahe are experiencing incredible growth rates according to South Dakota Game, Fish and Parks (GFP) fisheries biologists. Dylan Gravenhof, Missouri River Fisheries Biologist, shared this update at the January GFP Commission meeting in Pierre.
Lake Oahe is an expansive waterbody, spanning across both North Dakota and South Dakota, and GFP breaks the South Dakota portion of the reservoir into two segments – Upper and Lower Oahe.
“Although it is the same system, those two ends of Oahe actually function very separately from one another, almost as two distinct fisheries,” said Gravenhof.
Lower Oahe extends from the face of the Oahe Dam in Pierre to the Highway 212 Bridge in Gettysburg near West Whitlock Recreation Area.
“The lower end is a lot deeper, a lot cleaner, cooler water, and less tributaries so less flow coming in,” detailed Gravenhof.
Upper Oahe begins at this same divide, and extends to the North Dakota border north of West Pollock Recreation Area.
“The upper end of Lake Oahe is generally shallower, muddier, and has some of those major tributaries such as the Grand River and Moreau River so it is generally a little warmer and a little more turbid,” explained Gravenhof.
Each fall, for two weeks fisheries staff place over 200 gill nets at random locations across the reservoir. These survey results are compiled across the fishery and used to provide a status update and shape fisheries management activity for the reservoir. While walleye abundance is at its highest since 2017, it is the growth rates on the lower end of the reservoir that has fisheries biologists excited.
Survey results revealed about 5 walleyes per net, which continues a strong increasing trend for the lower end of the reservoir. This is the highest walleye abundance on the lower end of the reservoir since 2017, with a strong number of fish greater than 20 inches, many of the fish between 15-20 inches, and a slightly lower number of fish between 10-15 inches.
Fish less than 10 inches are too small to be caught in the sampling nets, which makes these 10-15 inch fish an indicator for upcoming year classes. While seeing most of the fish between 15-20 inches is exciting, as these are the “bread and butter” according to Gravenhof, the decreased number of fish between 10-15 inches is actually a cause for excitement, not concern.
This is because walleye growth rates have rapidly been increasing on the lower end of the reservoir. Traditionally, fisheries biologists look for an age-3 walleye to be right at 15 inches. In the 2025 survey results, walleye were reaching 16.9 inches by age-3. This is two inches greater than the 15 inch target.
“The quicker we can get a walleye to grow to a harvestable size is a great benefit to the fishery,” stated Gravenhof. “It’s crazy to think about, a juvenile walleye that’s half an inch in three years is growing to this big, plump 17-inch fish, that’s something we’re really excited about.”
This continues a trend that has been taking place the last three years. In 2023, walleye growth rates on the lower end of Lake Oahe were just over 15 inches. In 2024, these growth rates increased to 16 inches. Now in 2025, walleyes are just shy of 17 inches.
A deeper dive into walleye growth by age tells an even more promising story, as walleyes by age-2 are reaching 15 inches. This means walleyes on the lower end of Lake Oahe are reaching the target age-3 length a whole year earlier.
A deeper look into walleye growth rates by age reveals walleyes are reaching 11.7 inches by age-1, 15 inches by age-2, 16.9 inches by age-3, 18.3 inches by age-4, 18.9 inches by age-5, 19.1 inches by age-6, and then enter into the “over” class reaching 20.6 inches by age-7.
“Our fish are growing so quickly they’re not spending a whole lot of time in that 10-15 inch range, they’re maybe only spending a year in this range,” explained Gravenhof. “There’s not a lot of fish out there at that size for us to catch, whereas they’re growing really quickly into that 15-20 inch range and spending a few more years in there.”
This further reiterates why there is no cause for concern regarding the decreased number of fish between 10-15 inches, because this is only accounting for one year class, because these fish are growing so quickly. By contrast, there are between four and five year classes between 15-20 inches, which explains why the bulk of the fish fall into this category.
“You look at this and say ‘oh no we don’t have a lot of small fish’ but it actually makes sense they’re just growing really quickly,” stated Gravenhof.
Walleye condition is an equally important component in a healthy population, with a condition index of 80-90 considered healthy. The walleye condition on the lower end of Lake Oahe is right in the middle of this, indicating healthy walleyes and further supporting the excitement regarding walleye growth rates on the lower end of the reservoir.
These growth rates are supported by an abundance of forage for walleyes to feed on, including rainbow smelt, ciscoe, and gizzard shad. Rainbow smelt abundance has been extremely high, which continues the bounce back from the prey fish collapse following the 2011 and 2019 flooding and high water events.
By contrast, ciscoe numbers are not as high, which is what can be expected with the increasing smelt abundance. This is because ciscoe spawn in the late fall, where smelt come in early spring for their spawning ritual. This makes smelt a major predator on these new hatched ciscoes, which can suppress the population. This inverse relationship is currently favoring the smelt, following years of increased ciscoe numbers due to these decreased smelt numbers of previous years.
Forage information comes from high-tech acoustic surveys that are completed by GFP fisheries staff running transects in the middle of the night throughout the month of July. These acoustics produce both a number and sizes of these tens of thousands of fish, and the size by species is then confirmed by nettings of these forage species.
The combination of increasing walleye abundance and increasing forage numbers has fisheries biologists excited. The rapid growth rates further support this excitement, and these factors all point towards the lower end of the Lake Oahe walleye fishery being in fantastic condition.
Anglers should plan to take advantage of this opportunity, and enjoy what is shaping up to be one of the greatest years on the fishery in recent memory.
Lower Lake Oahe Walleye Growth by the Numbers
Approximate Lower Lake Oahe Walleye Length at Age-3
- 2023: 15 inches
- 2024: 16 inches
- 2025: 17 inches
Approximate Lower Lake Oahe Walleye Size by Age
- Age 1: 11.7 inches
- Age 2: 15 inches
- Age 3: 16.9 inches
- Age 4: 18.3 inches
- Age 5: 18.9 inches
- Age 6: 19.1 inches
- Age 7: 20.6 inches
Learn More About South Dakota Fisheries
Additional information regarding the fisheries in South Dakota, including status reports, forecasts, and deep dives into the data can be found on our South Dakota Fisheries Focus page.
