The graphical record of precipitation as recorded by Alberta Agriculture for the two townships that contain the Sylvan Lake watershed, plus a decade of lake level data measured by Environment Canada’s National Hydrological Service, are compiled here.
The surface of the lake received about 8 metres of cumulative precipitation in the period 2000-2016:
the maximum summer lake level remained close to 937 metres above sea level.
Where did all that 336 million cubic metres of water go that fell directly onto the 42 square kilometres of lake surface during that 16 years?
That’s not even the whole story. Of the 864 million cubic metres of water that fell on the surrounding 108 square kilometres of watershed land area, about 20-30% of it entered the lake as flow in the tributaries and roadside ditches.
The whole lake contains just 420 cubic metres of water, so a lot of water has come and gone in 16 years. On average, the lake is just 10 metres deep.
The answers to that question about water loss are that a small amount overflowed into Outlet Creek when it used to drain through Cygnet Lake on its way to the Red Deer River and Saskatchewan. Some of it become groundwater by infiltration. Most of it just evaporated. It went away. It didn’t stay around long enough to be sold or taxed.
You can see that natural evaporation process in action if you watch the lake surface carefully. Just concentrate. The lake level charts above show that about 0.25 metre of water disappeared after July 1. That was about 2 millimetres per day!