Question

what is the pH level of an average lake

Answer 1

Here is a site that explains what pH is all about and gives a somewhat lengthy explanation of pH and the pH of common chemicals. It goes on to say that there are many factors that control the pH in lakes and that the pH varies with season as well as during the daylight and evening hours. Finally they get around to saying that pH of most lakes is between 6.5 and 8.5.
http://lakeaccess.org/russ/pH.htm