Colorado is open for fishing 12 months a year, but a lot of the waters are not --covered with ice and inaccessible without skis or snowshoes during the winter. We have some good tail waters that remain open, but they can get a bit crowded on weekends. Dry fly fishing opportunities are brief and rare in the winter. Winter is is mostly nymphing, often with tiny midge patterns that are hard to tie on with shaking fingers. Still it beats being forced to stop fishing for months on end.