Accelorator Imobilised

Hi all I am new to this forum not sure if I am doing this right but here goes. I recently bought a Defender 110 pickup as a hobby for my son and myself, we recently went into a bog area and through a couple of puddles nothing deep, this it seems caused the accelorator to disengage we were however able to get home as the idle revs in the engin kept us at 10mph in 2nd/3rd gear. Later when the engin was switched off for a couple of hours the problem had gone, this has happened twice. I would appreciate any help.

Try unplugging the throttle pedal wiring connector and cleaning the contacts before plugging it all back together. Use a little petroleum jelly (vaseline) to stop the contacts corroding.
When you say not too deep - how deep?
Did the ECU get wet? Did the throttle pedal get wet? Did you get wet?

The TD5 suffers from the signal wire between the throttle pedal & ecu chafing through on the bulk head & causing intermittent throttle response that you are reporting.