See the lake level history as monitored by Environment Canada at the station in the WatersEdge Marina harbour.
The data may be viewed at this website too: https://rivers.alberta.ca/
The lake level dropped about 0.18 metres over the lake area of about 42 square kilometres. That is a volume decrease of 7.6 million cubic metres, although some of that was caused by cooling of the lake and its density increase.
Sylvan Lake Watershed Stewardship Society 