How waterproof is DJI Action 4

I am taking underwater video 1-4 feet deep in freshwater streams and rivers with the DJI Action 4. The camera is stationary and submerged for about 50 minutes. I've been using the waterproof housing but cannot seem to get past the issue of fogging, likely because these rivers are pretty cold compared to air temperature. Does anyone have experience leaving the Action 4 submerged for longer periods without the waterproof housing?