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Fly Fishing Harvey Gap – Colorado

Fly Fishing Harvey Gap – Colorado

Harvey Gap State Park is located on the western slope of Colorado, near the town of Silt. It is home to Grass Valley Reservoir, which offers some great fishing opportunities. Due to the variety of fish species here, there are a lot of options for everyone. Whether you like Bass, Trout or Pike – Harvey Gap has you covered.

Although Harvey is known for getting a lot of spin fisherman, fly fishers frequent here as well. Due to the large size of Harveys Northern Pike, it really attracts fly fishers hunting for their next big Pike. However, I have also caught nice Bass, Trout and Crappie here as well.

If you are looking for a good lake to fly fish, look no further than Harvey Gap. It is tucked into the Western Slope of Colorado, and often receives less fishing pressure than nearby areas. This is a state park, so it does cost $9 a day for an entry pass for each vehicle.

Fish Species At Harvey Gap

Harvey Gap is home to many fish species. Below, we will list the ones we’re aware of:

  • Northern Pike
  • Tiger Musky
  • Smallmouth Bass
  • Perch
  • Crappie
  • Rainbow Trout
  • Catfish

Grass Valley Reservoir offers a healthy habitat for a variety of species. However, most anglers frequenting here will be on the search for a large pike. They regularly reach 40 inches or longer, which is considered “trophy size” for any body of water.

There is also a population of Tiger Muskies here, which can be very difficult to catch. They were stocked in recent years, so they haven’t had the time to grow large yet.

The Smallmouth bass can easily reach 4-5 pounds, and you can find them in the bays and weed beds. They tend to like shallower water more than the other species.

The Perch and Crappie can reach good sizes, but most anglers don’t target them. You will often catch them by accident when you are hunting for other species.

Rainbow Trout at Harvey Gap can reach decent sizes, but they are usually between 12″-16″. Their population has a hard time here, because the Pike usually eat them before they can grow.

There are Catfish at Harvey, and they usually hang out on the bottom. For this reason, they can be really hard to target with flies. The anglers that catch them are usually using corn, hot dogs, or some other bait.

Flies To Use At Harvey Gap

There are many flies that will work at Harvey, but fishing streamers is my preferred method. I like to use Perch imitations most of the time, especially when I’m targeting Pike. However, I will also fish Meat Whistles, Clouser Minnows, Sparkle Minnows, Dungeons, EP Flies, Goldies, Etc. Below, you can see what some of these flies look like.

As far as rods, lines, and leaders go – I usually fish an 8 or a 9 weight, fast action rod. I prefer sink tips or even full sinking fly lines. For tippet and leaders, 20 lb fluorocarbon is my go to. If you’re targeting large Pike, you may want to consider using Wire Bite tippet from Rio – However, you will often get less bites when using a wire leader. I find that 20 lb fluorocarbon works well, as long as you land the Pike quickly.

Best Months To Fish Here

Harvey Gap starts to thaw out in late April to May. During this time, the Northern Pike will be spawning in the bays and shallow areas. This is a good time to target large pike, but they can be sluggish with the cold water.

June and July are my favorite months to fish here. Water temps start to warm up, and the fish become more active. During these summer months, I will catch my best Bass and Pike on the fly!

August can be a slow month at Harvey. The water gets really warm, and the fish can become more sluggish. They will often sit much deeper in the lake, and they can be hard to target. August can also be a miserable time to fish here, as air temps can reach the high 90’s.

September and October can be good, as the water starts to cool off a bit. Fish get more active during these times, and they are more willing to chase flies.

Of course, you can ice fish in the winter here, and it is quite popular. However, fly fishing is not doable in the winter months.

Shore Fishing Vs Boat Fishing

You can definitely fly fish at Harvey Gap from the shore, but it can be tough. The hills and trees don’t give you a lot of room for a back cast. In order to fish Harvey more effectively, it is best to go in a boat.

You don’t need a fancy motor boat! I often bring my raft up to Harvey and row around and fly fish. Some people also use stand up paddle boards to do this. I also have friends with drift boats that use a trolling motor on Harvey Gap. There are many options when it comes to watercraft.

However, be prepared for a strict boat inspection before you’re allowed to launch. Harvey Gap employees work hard to prevent the spread of invasive species – such as Zebra mussels and Quagga mussels. It is always best to show up with a boat that is clean and dry.


Overall, Harvey Gap is a wonderful fishery that offers many species. Although you’ll have some tough days here, you will be rewarded if you fish it enough. I have gone many days without a fish, and then i’ll land a nice Pike. You just have to put the time in.

Make sure to have a 7, 8 or 9 weight fly rod with some sort of sink tip line. Large arbor reels are also a good choice, because these fish fight hard.