I learned this lesson many years ago while i was living near Austin Texas. I was fishing below the dam at lake Travis. probably only 100 yds downstream from the dam. They were only letting out a little water at the time, but enough to provide a decent current. I anchored my canoe in a back eddy and was fishing the main stream. When the horn sounded to notify fishers that more water was going to be release, I thought I would be OK since i was out of the main current. I was wrong. The increased flow turned my back eddy into part of the main flow. By the time I realized I neede to get out of there the water was pulling the boat so hard I could not pull up the anchor. It only took moments before the current was about to pull the boat under. Luckly I had a good knife on my belt. The line was so tight that as soon as i touched the knife to the rope it cut through and almost launched me downstream. I learned several good lessons that day.