Havasu Hangin' is correct,
Here is a quick link for that water impeller.
http://www.mercurypartsexpress.com/P...e/homepage.asp
I read somewhere that this same part can be purchased from NAPA auto parts for a considerably lower price, maybe worth looking into. Anyhow have the engine serial number ready and you will at least get an idea how much the kit costs for your particular boat. I think unless the housing is damaged, just get the rebuild kit which comes with the impeller, gaskets and a few other misc things.
Good luck