True or not, there is this little guy who lives in the Amazon River among other places.
http://en.wikipedia.org/wiki/Candiru
Although some candiru species have been known to grow to a size of 40 centimetres (16 in) in length, others are considerably smaller.
These smaller species are known for an alleged tendency to invade and parasitise the human urethra; however, despite ethnological reports dating back to the late 19th century,
[5] the first documented case of the removal of a candiru from a human urethra did not occur until 1997, and even that incident has remained a matter of controversy.