Open water warning

As summer starts to warm up, we are hearing warnings not to swim in open water.
When it's hot any expanse of water is inviting, if you can swim.
Before I go into why swimming in open water might be dangerous, I want to point out one thing, that seems to be overlooked time and again.  Reservoirs are 9 times out of 10 for the collection and storage of drinking water.  As such, you SHOULD NOT swim in them, as you are swimming in drinking water, but due to sheer size of reservoirs, there are places where there will be no notice pointing this out. So, stay out of them!
Now, on to why swimming in open water can be dangerous.  Often the bottom can not be seen, so you don't know what is under the water. Open water is usually running water, and therefore colder than you anticipate.  The cold water will cramp your muscles after a while.
If you are swimming in the sea, it is better to swim parallel to the shore rather than away from it, as you could hit a current that pulls you out to sea.
Please be safe if you do swim in open water, and it's probably best not to go alone if you do.