The lake is the centrepiece of the Yarrawonga-Mulwala area. Of course, it's a man-made weir on the River Murray, and while its main purpose is to assist in river flow management and allow water to be diverted to two major irrigation channels (one on each side of the river), it contributes a lot more to the area than this. Watersports make use of it and there are lots of fishermen around.
The waterbirds certainly appreciate it, too. There are still numerous tree trunks standing in the water. I read that these create highly productive breeding areas for fish.