Lake Victoria has important shipping routes. Ships ferry cargo between Kisumu, Port Bell / Kampala (Uganda), Mwanza (Tanzania) and smaller towns like Jinja, Bukoba and Musoma. This is a main route of supply of fuel for Uganda, West Tanzania and even the Eastern part of the Democratic Republic of Congo.
Unfortunately, the shipping companies are only offering cargo services. No passenger services exist from Kisumu. Apparently, few people recognize the tourism potential in this and at the same time can afford the investments in ships.
There is a ferry that can take vehicles between Luanda Kotieno (North of the Winam Gulf) to Mbita, a very pleasant 50 minute trip. This trip has its own page.