Clogged raw water
Clogged sea strainer.
Failed raw water
Remnants from previous impeller failures clogging somewhere downstream.
pump">raw water pump. (any sign of leakage there?)
Choked raw water system. (need a flush with Barnacle Buster or similar)
(Ignore extra "> characters above (if you can see them); I can't seem to edit them out... I type pump and it renders as pump">raw water pump... Strange???)