Oops ... I read "water pump" as the engine water pump, not impeller. If it
was me, I'd pull the boat out and hook up the muffs and garden hose. Could
be someone started the engine up with no water supply ... that burns out the
impeller. Or could be the engine water pump, or risers blocked, or
thermostat, or .... could even be a faulty temperature gauge. Anyway,
running it on the garden hose should give some insight into the problem.