Backroads Whistler offers guided tours, self guided tours (with shuttle) and canoe rentals for Alta Lake and the adjacent River of Golden Dreams. The latter is a 5km stretch of winding river with mountain views.
Paddling down the (usually) slow moving river offers a chance to see Whistler from a different perspective. Of course, there is the chance to spot wildlife as well.
The river runs fastest from mid June to early July, when the mountain snow is melting. Read this conditions guide before planning a trip or deciding between a guided or self guided adventure.
Note that parking is limited at the lake so walk or take the bus if you can (#10, #20, #25 BC Transit buses).