Many lakes in eastern South Dakota have expanded during the Landsat record that began in 1972. Lake Thompson is one that has displayed remarkable change in recent decades.
This part of South Dakota is in what is known as the Prairie Pothole Region (PPR). Numerous depressions in the land were left behind there after the most recent glacial retreat. These depressions are termed potholes and collect rainfall and snowmelt to form wetlands and ponds of varying size.
A wet period in the 1980s and several years in the 1990s resulted in dramatic filling of Lake Thompson, located about 50 kilometers west of Brookings, SD, along with other nearby lakes and sloughs. Lake Thompson is now South Dakota’s largest natural lake.
An aerial image from 1952 shows Lake Thompson as a wetland, with about one-third of it as open water. Landsat began observing the area in 1972 with multispectral imaging that includes visible and near-infrared bands, which are great at distinguishing open water from dry land.
Water levels have fallen somewhat since the 1990s but continue to fluctuate depending on annual precipitation. Some shoreline and shallow areas change between dry land, marshland, and open water.
Most lakes in the PPR are closed systems. That means they do not have an outlet for water to flow out. It also means they can change a lot based on variable rainfall and snowmelt from year to year. As these water bodies expand, they can connect to other water bodies that were previously disconnected.
From around the 1890s until the mid-1980s, most lakes around Lake Thompson were closed lakes, disconnected from one another. Above average precipitation in 1984 brought an increase in tributary inflow into the lakes of Kingsbury County. Above average rain continued for two more years, and a chain reaction began that went something like this: In April 1986, Spirit Lake overflowed and drained into Mud Lake. Mud Lake then overflowed, its water draining to Silver Lake by way of a drainage channel. Silver Lake then overflowed into Lake Thompson.
But that’s not all.
Lake Preston also overflowed around that time and drained into Lake Whitewood, which subsequently rose above its outlet and drained into Lake Thompson. By October 1986, Lake Thompson ceased to be a closed basin when it drained into the East Fork Vermillion River. Water from the East Fork Vermillion River subsequently flows into the Missouri River. This marked the first time Lake Thompson had overflowed in over 100 years.
The aerial photo from 1952 is black and white and doesn’t have the infrared imaging capability of Landsat, but it has something that Landsat doesn’t—very high resolution.
It’s possible to locate trees and buildings in this image. Zooming in to an area near the lake is a location that is cultivated cropland. The sharp corners mark the different fields.
Land here is divided into sections of 1 square mile. These extreme closeups show an area of land covering approximately six sections. This area shows three sections across and two sections high.
A closer look shows farm buildings, with a shelterbelt of trees beside them.
Later Landsat images reveal that those fields and structures are underwater.
* = Location of farm structures shown in the aerial photo closeup.
Lake Thompson is a crucial habitat for migratory birds. The simultaneous presence of open water, shallow mudflats, cattail marshes, and wet meadows offers a diverse landscape for shorebirds, waterfowl, wading birds, and gulls.
Herons and egrets use the shallow water and mudflats on the lake’s fringes. Pelicans, gulls, terns, and ducks thrive in the open water.
Besides affecting farmland and wildlife habitats, the expanding lake has flooded several roads. For example, 218th Street, also known as Oldham Grade, crosses the southern part of the lake. It was closed for much of the 1990s. It is open again, but the area’s roads often need repair from the high water.
Landsat data can be used to map these changes and help organizations like South Dakota Game, Fish, and Parks understand the interaction between lake levels and wildlife populations.
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