Not limited to stagnant water!

Map of the states where deaths have occurred (CA is on the list):

http://www.cdc.gov/parasites/naegleria/state-map.html

The bacteria exists in running water too:

http://www.cnn.com/2011/HEALTH/08/17/amoeba.kids.deaths/index.html

There used to be a sign at Arizona Hot Springs or Ringbolt Hot Springs about not submerging into the pools:

http://www.yelp.com/biz/arizona-hot-springs-boulder-city