This prior question talks about natural estrogen (TL;DR: Months to years): How quickly do estrogens break down in the environment?
A lot of media has said, "birth control hormones in the water!!!!" Ethinyl estradiol (EE2), is a synthetic hormone
Conversely, a birth control advocacy group, says, "Naw, it's a very small part of the total estrogen load in the environment."
(can't post more than two links) :P
What I recall reading was that one of the types of birth control hormones got processed by the human body, looked like it was changed (in the urine, etc), and so they were fine with it not causing an issue - but when it got into the environment, it rapidly got changed back into the (estrogen?) it was originally - and thus caused problems.
I'd like a nice summary of what's thought to be going on, preferably from a more neutral source.