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Lake Agassiz Plain

Last updated: February 9th, 2026

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Name	†	Color on Map	EPA Code‡
Glacial Lake Agassiz Basin	○		48a
Beach Ridges and Sand Deltas	○		48b
Saline Area	○		48c
Lake Agassiz Plains	○		48d

† Status: ✓ = Complete ○ = Needs Image … = Incomplete ∅ = Stub Only

‡ This code refers to the US EPA's Level 4 ecoregion codes for the continental U.S., see here.

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↑About the Lake Agassiz Plain

The Lake Agassiz Plain, referred to as the Lake Manitoba and Lake Agassiz Plain in some documents, is a region extending from around Daupin Lake, Ontario, southward a bit past Fargo, North Dakota, and extending slightly into adjacent areas of Minnesota as well.

The climate is a severe mid-latitude humid continental climate. The location near the east-west center of the continent and distance from mountain ranges leads this region to have some of the coldest winters relative to its latitude, as polar masses tend to be centered roughly over this region as they push southward. However, the area is also subject to unusual warm spells at any time of year. Precipitation is seasonal, falling mostly in summer owing primarily to temperature, but there are also great fluctuations in humidity from one year to another and sometimes also over time scales of weeks or months. Relative to the severity of winters, the frost-free season is relatively long. Although temperatures decrease moving northward through this region, summer temperatures only decrease slightly, whereas winter temperatures are dramatically colder, averaging around 25-30°F (11-17°C) colder in the north. Even the south of this region, however, has some of the coldest winters anywhere in the lower 48 US. Summer brings frequent thunderstorms; although "tornado alley" with the peak frequency of tornadoes lies farther south, this area still has a relatively high risk of tornadoes accompanying summer storms.

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