Carbon fibre structures
MJB
Provided that the structure is not fractured it may* be OK. The biggest threat to laminated composites is from impact damage which causes delaminations between the plies. These can be tricky to spot because carbon fibre materials are linear elastic to failure, in other words they do not bend, they either break or spring back to their original position. Unfortunately the same is true for the layers over a delamination, so they are not visible. You need ultrasonic NDI or a tap hammer to find them.
The other problem is that depending on the resin type used, impcat damage can occur at quite low impact energy. Simple tool drop accidents can result in significant delaminations. Provided he didn't hit the water too hard it may be OK.
Blakmax