I love (love), climbs to Alpine dams/lakes. And the ascent to Lac de Moiry has to be one of the hardest. 2100 metres (7000 feet), hard work.
I took the harder but quieter route via Vercorin – it adds 300 metres of climbing but has far less traffic. See the map for the easier route, which I used for the descent.
The Valais region of Switzerland is full of fantastic climbs to glacier dams/lakes. See here for some of my favourites.
The last steep stretch before the dam includes a long, wet tunnel (boo!).
Once at the lake (2250 metres), the road continues for four more easy kms to 2350 metres. Definitely worth the effort as it leads to a small lake and views of the nearby glacier.
Despite tired legs, I took the long-cut down, first visiting the resort of Vinal, which was a mountain top finish the 2009 Tour de Romandie:
A superb route.