Here's the word from Idaho Fish and Game. Not that anyone would want to camp next to a beautiful reservoir on a lovely, sunny September or October weekend. That would be horrible, wouldn't it?
Fishing and other day-use activities are unaffected by the campground closure, which has been in place for the past three years. Camping at Horsethief Reservoir is permitted only between May 1 and Sept. 20 each year. Seasonal closures are not unique as many Idaho state parks and national forest lands are closed, or soon will be, for the winter. Horsethief Reservoir is one of the few developed campgrounds where no fee is charged, contributing to its popularity. In the 1990s, Horsethief’s camping areas were developed to limit resource damage from unregulated use. Since then, Idaho Fish and Game has staffed Horsethief with camp hosts for the peak fishing and camping season. Because of limited resources, camp host services, maintenance services and camping end mid-September each year.