Water Circulating Pump?

What would happen if your pump was to go out?

I bought boat a few months ago and my Mech told me that I would need to replace it soon, well I put it off and now my boat is acting up. We launched yesterday and idled around no problem, started up, went into gear, got into the water told them to hit it and nothing... As soon as my friend tried to take off the boat started to bog down and would not come up to speed. Its going in the shop today but I am figuring that my pump finally went. Its always something...

also, would this make my engine "whine" when it is put in reverse?