- Location: Sevier County
- Directions: 25 mi southeast of Richfield via SR 24
- Type: Fishing
- Size: 420 acres at full pool
- Elevation: 6,995 feet
- Hours: No restrictions
- Likely catch: Cutthroat Trout, Rainbow Trout
- Possible catch: Brook Trout, Tiger Trout
- Regulations: To see what statewide or special regulations apply to this waterbody, please read the current Fishing Guidebook.
- Site amenities: No improved facilities. Small boats can be launched from shore when the water level is high. Public access and primitive camping is available on BLM lands along the west shore.
- Handicap access:
- Site description: In fall 2008, irrigation demands led to a very low water level and numerous fish were observed exiting the reservoir. The Division of Wildlife Resources will conduct samples in the spring to determine how much the low water level impacted the fishery. Water draw-downs are a relatively common occurrence at Koosharem and a few trout generally make it through.
Koosharem Reservoir sits near the head of the Otter Creek drainage in a relatively shallow basin. Shallow water promotes heavy aquatic weed growth by midsummer and provides excellent habitat for Utah chubs. Chubs have been a long-term problem and can limit the trout fishery when they become over abundant. Chemical treatments with rotenone to temporarily remove chubs were conducted in 1959, 1969, 1977, 1985 and 2002. Extensive marshes and springs above the reservoir have prevented complete removal of chubs from this drainage.
Koosharem Reservoir can be an excellent trout producer during four- to five-year periods after rotenone treatments and during high water years. There is no conservation pool in this reservoir and it can be drained to very low levels. However, there is usually enough water retained to carry some trout over from one year to the next. With good conditions, trout ranging up to two or three pounds can be common.
Following the 2002 treatment, Bear Lake Bonneville cutthroat trout became a regular part of the stocking program because they are known to prey on chubs. Although it is unlikely that cutthroat trout will control chub numbers in this shallow weedy reservoir, they are likely to use chubs more as a food source than rainbow trout. Just over 10,000 cutthroat trout and 10,000 rainbow trout (five- to seven-inch fish) have been stocked annually in recent years.
Some hybrid tiger trout (brown trout/brook trout cross) have also been stocked on an experimental basis to see how they perform in association with high chub numbers. Brook trout occasionally migrate into the reservoir from the upstream drainage and supplement the fishery. Rainbow trout are commonly caught by shore anglers fishing with commercially prepared baits. Cutthroat, tiger trout, and brook trout are more likely to be caught with flies and lures, or natural baits such as worms, grasshoppers, or dead minnows.
Other nearby waters include Fish Lake (15 miles to the east) and Otter Creek Reservoir (25 miles to the south).