it gets drained and cleaned once a year. and in true san antonio fashion it is an event with a mud king and queen each year. truth is not many people, outside of those under the influence, fall in. i've been down there during the holidays, when it is the busiest, and had no problems.
oh and the paseo del rio organization responsible for the rivers uptake did modify how they cleaned the surface on a daily basis after cuban's comments. truth is riverwalk's allure isn't the river. it's the restaurants and shops and bars along it's banks.
Believe half of what you see and none that you hear.