Yes, this is what it sounds like: competitors paddle tin baths around Castletown's Middle Harbour to raise money for local charities. There are men's, ladies and team races.
There is also the Snake Race, which seems to consist of teams of six (four men, two women) competing as a team in some form of construction of type inner tubes.
If you like water (include me out!) it looks like fun.
As always there is more on the World Tin Bath Championships website at www.castletown.org.im/tinbaths/.