If you are planning a trip to Heenan Lake, then take note of the following: the lake opens for fishing on the Friday of Labor Day weekend and closes on the last Saturday of October (unless it falls on October 31st, then it's the Saturday prior). During that period, Fridays, Saturdays, and Sundays are the only days anglers are permitted to fish.
Rainbows Swimming in the Lahontans' Family Pool
A fisheries biologist with the California Department of Fish and Game has confirmed it: Hybridized rainbows and cutthroats are present in Heenan Creek and they do move downstream into Heenan Lake.
John Hanson a biologist with the Heritage and Wild Trout Program responsed to my query with background on the issue as well as CDFGs safeguards to manage the integrity of the Lahontan broodstock at Heenan. I've included his response in full below.
Thank you for letting me know that you have caught rainbows in Heenan Lake. Hybridized rainbow and cutthroats are present in Heenan Creek above the spawning shed on the east end of the lake. These fish can move downstream into the lake. The hybridized fish are taking on more and more rainbow characteristics and appear they are becoming more prevalent in the lake.
I am sure that they do compete with the Lahontan cutthroat trout.
To insure that they do not hybridize with the Heenan Lake cutthroats, we take fertilize the eggs at the spawning shed and raise them for a year at Hot Creek Hatchery. Before we stock them back into Heenan, we clip off the adipose fin to mark the fish for future spawning. We spawn only the adipose fin clip fish to insure we do not cross the two populations. This summer we started to remove the hybridized population from the creek. This could take some time since we are using electrofishing to remove the fish from the stream and we can not get 100 percent removal during one season. We will need to do this over several years.
Two thing that you could do to help the Department out is to note on the angler survey form how many rainbows you caught while fishing Heenan and to note if the adipose fins is present (fin directly in front of the caudal fin).
Associate Fisheries Biologist
Heritage and Wild Trout Program