Travel to Bukavu

Goma[ is not considered safe but there are boats every day. Expect to pay $10 - $50 depending on speed / comfort. If you're white you may have to argue to get a cheap ticket, apparently it's 'not suitable for tourists'. You may have to pay $5 departure tax - they gave me a receipt so I suspect it's official but you never know here. Occasionally these boats also stop at Idjwi Island

There are wooden boats to Idjwi island leaving at various times through the day. Ask around at the port. Unlike the northern part of the lake the water here is generally calmer (due to it being narrow and populated with a high number of islands) so the voyage by wooden boat is not usually unduly traumatic