Shellmouth Reservoir

{{Short description|Reservoir in Western Canada}}

{{Use Canadian English|date= October 2023}}

{{Use dmy dates|date= October 2023}}

{{Infobox body of water

| name = Lake of the Prairies

| image = LakeofthePrairies1.JPG

| image_size = 255

| caption = Lake of the Prairies from the Shellmouth Dam

| image_bathymetry =

| caption_bathymetry =

| location = R.M. of Shellmouth-Boulton / R.M. of Shell River, Manitoba and Cote No. 271, Saskatchewan

| coords = {{coord|51|08|40|N|101|30|19|W|type:waterbody_region:CA-MB_scale:250000|display=inline,title}}

| type = reservoir

| inflow = Shell River

| outflow = Assiniboine River

| catchment =

| basin_countries = Canada

| pushpin_map = Manitoba#Canada

| pushpin_map_caption = Location in Manitoba

| length = {{convert|56|km|abbr=on}}

| width =

| area = {{convert|61.5|km2|abbr=on}}

| depth =

| max-depth =

| volume = {{convert|480|e6m3|acre.ft|abbr=on}}

| residence_time =

| shore =

| elevation = {{convert|425|m|ft|abbr=on}}

| frozen =

| islands =

| cities =

| other_name = Shellmouth Reservoir

| reference = {{cite web |url=https://www.gov.mb.ca/mit/wms/shellmouth/ |title=Manitoba Infrastructure: Shellmouth Dam and Reservoir |publisher=Government of Manitoba |access-date=November 22, 2021}}

| module = {{Infobox dam

| embed = yes

| name = Shellmouth Dam

| image = Shellmouth.jpg

| image_caption = An aerial view of Shellmouth Dam and Reservoir

| coordinates = {{coord|50|57|49|N|101|25|07|W|type:landmark_region:CA-MB_scale:10000|display=inline}}

| builder = Prairie Farm Rehabilitation Administration

| status = O

| dam_type = Embankment dam

| construction_began = 1964

| opening = 1971

| cost = $10.8 m CAD

| owner = Government of Manitoba

| dam_height_foundation = {{convert|21.3|m|ft|abbr=on}}

| dam_width_crest = {{convert|1,270|m|ft|abbr=on}}

| purpose = Multi-purpose

| website = [https://gov.mb.ca/mit/wms/shellmouth/ gov.mb.ca/mit/wms/shellmouth/]

}}

}}

The Shellmouth Reservoir (also known as Lake of the Prairies) is a man-made reservoir on the Assiniboine River in Manitoba and Saskatchewan, Canada.{{Cite web|title=Water Management and Structures {{!}} Infrastructure {{!}} Province of Manitoba|url=https://www.gov.mb.ca/mit/wms/shellmouth/|access-date=2021-08-07|website=www.gov.mb.ca|language=en}}

The Shellmouth Dam ({{coord|50|57|49|N|101|25|07|W|scale:10000}}) is a multi-purpose embankment dam built by the Prairie Farm Rehabilitation Administration (PFRA).

The dam and reservoir are part of a strategy to reduce the risk of flood damage for Winnipeg and other communities along the Assiniboine River. For example, in the 1997 Red River flood, the inflow to the reservoir peaked at {{convert|10000|cuft/s|m3/s}} while the outflow never exceeded {{convert|1700|cuft/s|m3/s|abbr=on}}.{{cite web |title=Flood Control Works |website=Prairiewaternews.ca |url=http://www.prairiewaternews.ca/water/vol7no2/story2.html |url-status=dead |archive-date=January 15, 2013 |archive-url=https://archive.today/20130115121505/http://www.prairiewaternews.ca/water/vol7no2/story2.html}} The reservoir is also used to supplement flows on the Assiniboine when conditions are dry, ensuring water supply for Brandon, Portage la Prairie, irrigators, and some industries. For example in early August, 2021 the flow in Brandon was a little over 9 m³/s while the outflow from Shellmouth was 5.7 m³/s and inflow was less than 0.5 m³/s. Therefore without the dam the flow in the Assiniboine at Brandon would be a bit under 4 m³/s.

Asessippi Provincial Park is established around the southern arm of the lake.