When to Change Impellor??

I have 150 hrs on my 2000 C60. When should I have the impellor changed? The boat runs in the tidal Potomac well above the salt line. Another question, is the impellor and water pump the same thing?

Thanks for any responses.

[boats.net]

Water pump impeller(or water pump kit if needed) should be changed every 2 years.

Impellor change

Thank you very much, I guess I had better do it.