I have been talking to lots of anglers. Couple being guides and others being hard core anglers.
ALL of them have seen the exact same thing as I have.
The population of brook trout has taken a serious decline in the last 2 years.
I have done an informal testing of the streams that I typically catch brook trout in. I see a 70 percent decline in the brook trout population. In 9 of 10 of my brook trout streams I have found gill lice. The biologists and trout experts I talked to say that gill lice alone can not decimate a population of brook trout but gill lice and other factors can. The other factors being floods, over population, and long periods of excessive heat.
Brook trout and rainbows are hosts to gill lice not browns. Gill lice are not harmful to humans.
Below is Wisconsin's Department Of Natural Resources lead "Trout Expert" contact info
Matthew G. Mitro, Ph.D.
Fisheries Research Scientist
Wisconsin DNR Bureau of Science Services
2801 Progress Road
Madison WI 53716-3339