I would never run my 30K plus Kubota in any water over the axles. The ingestion of water into the axle cases due to the vacuum produced by the cooling effect of the water on the warm castings will compromise the oil in the axles and will eventually destroy the gears, bearings and seals.
Above and beyond that, any ingestion of water into a diesel engine will immediately destroy it. A diesel, due to it's high compression ratio will hydraulic lock with the introduction of water into the combustion chamber. At the very least, you will destroy the crankshaft, break a rod or ventilate the block.
After that, you might just as well leave the tractor in the pond. Sort of an underwater reef for fish to habitate in!!!