The race starts at 12.30pm at the Whanganui East boat ramp and ends at the Putiki Slipway 3.5km downriver. The tide should be going out.
There will be prizes for the fastest raft, the most creative craft and the crew with the best costumes. Each of the major prizes is worth $300.
The prizegiving takes place at Putiki Park straight after the race.
It costs $50 per raft to enter, with money going to Plunket as a local charity.
Mr Goldsworthy's Plumber Dan business has a team entered.
The crew have been building The Floater in their spare time, a contraption of plastic barrels and plumbing downpipe. They're not sure it will actually float.
"It will eventually be brown. We may paint it," Peter Ellery said.
There are rules for entrants:
¦Each team must have at least four people, and all must wear life jackets.
¦Polystyrene can't be used in the rafts, unless it's enclosed, because it can break up and make a mess in the river.
¦No alcohol, and no motorised propulsion.
There are 26 entries so far, and they close on March 1.
¦To enter, see Mr Goldsworthy at the Saturday market, call him on 021 635 517 or email plumberdanltd@gmail.com.