The only place within 1 hour of St. George with an alpine setting is Pine Valley Reservoir. It is very small and it hit hard (fished a lot). It is so small, I'm not sure a boat is allowed (only small boats if that). It is about 45 minutes away. There is also Baker Dam Reservoir. It holds trout, but is not really in an Alpine setting....more like cedar/juniper trees. It is 30 minutes away.
You will have to drive 2+ hours to get a good experience. The Boulder Mntns (near Boulder and Escalante) are awesome (great fishing, scenery, hiking, many alpine lakes, etc.), but they are about 4 hours away. They also get hit hard in the summer. Oiled roads to many areas at first, then dirt roads and trails only to many lakes. This would be my first choice, heads and shoulders above anything else.
The Beaver mountain (listed as the Tushar Mountains on topo maps) is 2 1/2 hours from St. George. It has about 7 - 10 lakes (depending on what you call a lake), is beautiful, in the pines, has o.k. fishing, but A LOT of people go there, especially from Nevada. The fish on average are quite small. Oiled roads up Beaver canyon, then dirt road to all of the lakes but one.
Tropic Reservoir is about 2.5 - 3 hours away and offers good fishing, alpine environment, etc. Another lake closeby to that one is Pine Lake, Northeast of Bryce Canyon N.P. (same qualities but smaller fish). These are both close to Bryce Canyon National Park (you can see it from Pine Lake). You could visit and hike it while you were there. Oiled most of the way, dirt near the end. These lakes are not hit as hard, but are not remote by any means.
Another nice place is Yankee Meadow. It is up Parowan Canyon, about 1.5 hrs away. Decent fishing, pine trees, etc. but gets hit hard as well during the summer. Oiled road up the canyon, then dirt road the rest of the way.
Navajo Lake is picturesque as well (especially from the road above). It is considerably larger than the other lakes and receives less pressure (in my opinion), but you will still see quite a few people. It has good fishing depending on the day. It has very easy access via an oiled road up the canyon and then dirt road by the lake. I have hiked to a waterfall nearby, but don't remember the name. 1.5 hrs away.
Nearby there (further up Cedar canyon) is Duck Creek pond/lake and Aspen Mirror Lake. These small lakes/ponds are very pretty, in the pines, but I don't think boats are allowed on either. Nice hiking in the area. 1.5 hours away. Both have good dry fly action.
Panguitch Lake is closeby as well, with good fishing, and in the pines. The other areas are more picturesque and the pines are not along the lake, but you are at that elevation if you camp elsewhere. It is about 1.5 - 2 hours away. Size restrictions are in place.
Another option is Kolob Reservoir. It is in the pines, and has great fishing (sometimes slow). It has special regulations, however: artificial fly and lure only, with size restrictions. It is not as picturesque in my opinion, but is still quite pretty. It is a small tradeoff for better fishing. Take the road north from Virgin. 1.5 hours away.
Another great place is Fish Lake, S.E. of Richfield. It fills your requirements nicely. It recieves quite a bit of pressure, but is very large and can handle it. There are other lakes nearby as well (Forsyth, etc). 3 hours.
Another closeby lake, but in the junipers is Paragonah Reservoir (sometimes listed as Red Creek Res.). It is up Paragonah Canyon. It has many, many fish, but most are small. It can have very fast fishing and needs the pressure to reduce the population. It is not as pretty. It receives far less pressure than the other lakes. It is about 1.5 hrs away and it has a so-so dirt road up to the lake.
Enterprise reservoir is closeby as well. It is in the pines. It has catchable rainbows. One of the reservoirs is drained for repairs. It is pretty here as well, but the fishing is poor (in my opinion).
There are other lakes that have far better fishing, but aren't in an alpine setting. I'm sure I'm forgetting some places as well, but these will start you out. If you have the time, go to the Boulders. It is also the only area on this list that offers hiking into the lakes.
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