Do you know how much water is in that river? It isn't all that large. Do you know how much of the water is already spoken for by various canals and city water treatment plants? Do you know whether any of the water in that river is actually available?

Same thing with the lake. The lake is the only supply of water to the river. You can't just pump a bunch of water out of the lake without cutting out the people downstream who need the water from the river.

This is Utah. It's a desert. Water's not a real plentiful commodity out here. It's precious and scarce. Most of the easy answers don't work. (If they did, somebody else would already be using the water from that source.)