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Chapter 16: Water Resources

16.54: The Shellmouth Dam and Lake of the Prairies

The Shellmouth Dam 1 built across the Assiniboine River 2 and completed in 1967 is part of a three-pronged strategy—the Red River Floodway, and the Portage Floodway are the other two—to reduce flooding at Winnipeg. It also provides flood protection to Brandon and Portage la Prairie as well as ensuring a reliable flow during the summer through these cities that get their municipal water supply from the Assiniboine. The area has also become the location of an attractive provincial park—Asessippi Park—that provides opportunities for fishing, boating, camping, and associated activities. Blackbird Creek 3 and Bell Creek 4 flow into the Assiniboine from the north dissecting the north wall of the Assiniboine Glacial Spillway.

The dam backs up water into the Assiniboine 5 and Shell 6 valleys creating Lake of the Prairies 7 that extends north and west into Saskatchewan. The dam’s spillway can be seen at the northwest end 8, and a riparian channel 9 carries water into the meandering Assiniboine 10 which flows west then south past Shellmouth 11 located on a terrace 12 above the spillway floor.

The dam carries PR 482 13 across the Assiniboine; it then runs north 14 past Dropmore 15 and on into Saskatchewan. Another east/west gravel road 16 bends down the east wall of the spillway 17, and then passes through Shellmouth 18 and up the west wall of the spillway 19. The CN railway line 20—now abandoned—runs through Shellmouth; across the spillway 21, along the west side of Lake of the Prairies 22, and then past Dropmore 23 and into Saskatchewan.

This photo covers the Manitoba/Saskatchewan border 24 that runs along the 29/30WI range line. At the northern boundary of township 22, this line jogs west about 1¼ miles (2 km) 25. This jog is repeated every four townships north from the 49th parallel, starting at the township line between township 2 and township 3 and finishing at 56ºN, from where it is a straight line following the 106ºW line of longitude.[i]

Figure 16.54: The Shellmouth Dam and Lake of the Prairies

Figure 16.54: The Shellmouth Dam and Lake of the Prairies

Figure 16.54

Vertical air photograph: A25047-21

Flight height: 24,700 feet a.s.l.; lens focal length: 6 inches

Scale: 1:50,700 (approx.)

Date: August 5, 1978

Location: Townships 22 and 23; Ranges 29 and 30WI

Map sheets: 1:250,000 62K Riding Mountain

                    1:50,000 62K/14 Inglis


[i] Welsted, J. “Straight or Crooked: An Assessment of Manitoba’s Boundaries” in The Yorkton Papers: Research by Prairie Geographers eds. J. Welsted and J. Everitt. Brandon: Brandon University, Department of Geography. 1997, 180-190.