Submarine Hole is a Class IV+ rapid located at mile 20. 5 on the Illinois River, known for its reputation of flipping rafts at all water levels due to a large plug rock at the bottom and narrow exit slot.

At low flows, the passage between the left wall and plug rock is very narrow, while at high flows the rock creates a monster reversal; the recommended approach is to enter far right and work left to the narrow exit slot.

This rapid requires careful boat control and is best scouted from the left bank before running.