Racecourse is year-round but you don't see many people up there between November and March, water temp under 40 now. But February afternoons are pretty warm here.
Another spot not as good for play but a scenic II+ is Rio Chama day run up above Abiquiu. Free access, camping, etc. Its not running yet, but they get dam releases most week-ends in the summer. High water there is April/May.