You have chosen to take the easiest route which is to wade across shallow water. Upon reaching the waters edge you observe that this underwater river is wider than anticipated. By the time you reach the center the water is waist level and the current slows your progress. Trudging ahead you feel a stinging pain on your toe. You must have stubbed it on the rocky river bottom. Now you feel pain in your other foot. You are being bitten! Much worse than that, you are being eaten. Holding up your hand you're horrified to see missing fingers.
You have disturbed a school of flesh eating fish. They are fairly quick to devour you, although you wish it would have been much quicker!