Aussie report on Crocodylus porosus, the Saltwater Crocodile. They attached data recorders to the backs of 14 different crocodiles, ended up recovering nine of them, and discovered among other things, that the crocs could dive as deep as 50 feet. The post mentions that there isn’t much if any data on the diving behavior for this animal.
’
Related study on a smaller species of crocodile, C. johnstoni: Ecological and physiological determinants of dive duration in the freshwater crocodile, Functional Ecology 2010, 24, 103–111. I’m stunned that Wiley made the full text available for free, but there you are. Not as deep a diver—of course, that could just be due to the river being much shallower than the bay where the Saltie study was done. But very long duration for some of them: one was on the bottom for ~400 minutes.