Originally Posted by jwalker
Do you know what nautical charts are?
That may sound a bit harsh, but 'tis good implied advice.
Local knowledge is can never be under-estimated, and walking the banks of rivers and estuaries at low water springs can be valuable both for seeing the route that a river bed takes and what hazards are covered by the water at high tide.
I guess that you have an alloy prop - have a close look for any damage. If it looks like it's been clonked, don't try to mend it yourself (unless you've done this sort of thing before) but take it to a specialist.