Rock Lake, Manitoba

Rock Lake is in southwest Manitoba, near Pilot Mound, about 200 kilometers southwest of Winnipeg. The north shore is in the RM of Argyle and the south shore is in the RM of Roblin. The Pembina River runs through the lake. 

It is about 8 miles long and 0.75 miles wide with a surface area of about 6.6 square miles and has an average depth of 2.5 meters (8 feet) when the lake is at 1329 feet (405.08 meters). The deepest point is 1317.7 feet (401.63 meters) or about 11.3 feet deep when the lake is at the normal summer target level of 1329.0 feet. The drainage area is about 1800 square miles. The lake is fed by four main tributaries; the Pembina River, Long River, Whitemud Creek and Badger Creek. 

The valley was formed when melt waters from glacial Lake Souris cut into shale bedrock as they spilled eastward into Lake Agassiz. Over time tributary streams flowing into the valley have deposited sediments over the valley floor forming natural dams. These dams caused the creation of the series of shallow lakes we see today, Pelican Lake, Lorne and Louise Lakes, Rock Lake and Swan Lake.

Rock Lake has a long recreational history dating back to the early 1900's. There are about 125 cottages on the lake and a camp run by the United Church. Before 1941 levels dropped to as low as 1324. A stop log dam was built about three miles downstream of the lake to regulate levels. From 1941 to about 1951 the target level was 1327 feet. Since 1963 the target level was 1329. Schemes to raise the lake as high as 1337 have been considered. The river channel has become so silted up that the dam is no longer operational.