They say it takes some training. And there can be risks, like running when your feet are too cold to feel if you get injured.

VOA: special.2010.02.03

"Without giving too much away, I don't think you can go through something like that without it affecting you."

VOA: standard.2010.05.04

"If you have an imbalance, or literally too much nitrogen and too much phosphorous getting into those systems, you can essentially deplete the oxygen in that water.

VOA: standard.2010.08.04