On Sunday, the Aqua, a luxury river cruising boat just beginning a turn down the Amazon, was boarded and raided by six weapon-yielding bandits who robbed the vessel's 24 passengers of money and other valuables. Luckily that's all the pirates took as no cruisers were hurt.River cruise line website. Map is from that site.
Nigeria also has river pirates, as reportedly do Russia, Romania and, as you see if you look to the updates to this post, did the Mississippi River and California's Sacramento River.
UPDATE: Simpler times: