What would be really lovely is an evening cruse from Lausanne - boat (la Suisse - belle époque boat) leaves Lausanne-Ouchy at 1845 and returns at 2100. There is a nice restaurant on board (get a First class ticket) and you will see the sunset over the Jura and once it is dark, the lights of Evian and Lausanne twinkling over the lake. There are also day time cruises. See the link to the cgn site that swissaholic gave above.
Thank you. Since I have a Swiss Pass, how does one make reservations for one of the cruises if we don't want to go first class or have a meal? Or if we do decide to have the meal?
You don't ! No reservations are needed for the boat. Swiss Travel Pass covers the boat ticket 100% - just show it when boarding or when tickets are checked. For the restaurant - go there when you board and get a table. However the restaurant is on the top deck (as far as I remember) and top deck is 1st class. So you would need to upgrade to sit in the restaurant. You can do this onboard. if you don't want to eat upgrade anyway because the views are better from the top deck.
Thank you for your detailed explanation.