Reservations may no longer be available at the campsites but there may be places to stay along the way to Walden, in Walden, or even in Poudre Canyon.
A few of us are planning on one day trips to go there and fish with the groups that are camping so even if you aren't staying for a few days come on up and join in the fun. It's about 1.5 hours drive time from where you turn off of Hwy 287 to go up Poudre Canyon depending on whether you make stops to fish on the way or just stretch your legs along the river or make a pit stop at the Moose Visitors Center.
Ranger Lakes and North Michigan Reservoir are both Colorado State Parks and require either an Annual or Daily Pass. No water craft on Ranger Lakes, shore fishing only but boats are allowed on North Michigan Reservoir.