Re: Cache la Poudre River, Fort Collins?
From Greeley it would probably be closer to just go west on hwy 34 toward Estes Park, the road follows the Big Thompson river.
Just above Estes is the Rocky Mtn NP and there is a lot of water up there to explore, especially if you're into hiking.
Something to think about is that as you head west on hwy 34 after you pass through Loveland, watch for hwy 56 on the right, if you take that road north, it heads up to Masonville (a wide spot in the road), take a left turn and that puts you on hwy 27, if you follow that north it will take you up to hwy 14 that runs through Poudre Canyon (about 20 miles up the canyon).
There are numerous small lakes in and around that portion of the front range, do some exploring and you will find some great bass and carp fishing.