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Lucky Peak is being drawn down 125 feet to do repairs on the Turner Gulch boat ramp. The low water levels in Lucky Peak will impact water temperatures on the Boise river this August. Water temperatures on the whole river are expected to rise and stay above 66 degrees for several weeks, which is very hard on trout.

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The US Army Corps has started down Lucky Peak in order to do a repair on the Turner Gulch boat ramp, which means by the end of August, there will be no ramps available.  The Lucky Peak Dam and Lake – WallaWallaUSACE Facebook Page recently posted this warning:

BOATERS - Remember to be very cautious about any long term mooring, beaching, or anchoring as the continued fall of the lake is about 2’ per day. No salvage services are available and if your boat becomes stranded it will likely remain until the spring fill so be careful.

The figure below shows the current elevation of the reservoir (as of 7/27/24) and the different boat ramps. You can find the latest version of this graph under the "Boat Ramps" section of BVFF's Local Waters web page.

BOISE RIVER FLOWS

Flows on the main Boise through town are not expected to rise during the drawdown. The drawdown is being achieved by reducing inflows from Arrowrock and Anderson Ranch Reservoirs (Arrowrock cut inflows first and Anderson will reduce flows the 3rd week of August). This approach allows them to maintain the water in upstream reservoirs for future irrigation needs.

LUCKY PEAK OUTFLOW ZONE

Tailwaters like Lucky Peak and Anderson Ranch Dam usually release cold water all summer long because the water is coming out of the bottom below the thermocline where water is colder. However, the Lucky Peak drawdown will bring the warmer surface epilimnion layer of water into the outlet zone which will increase the temperature of outflows.

2024 EARLY AND DEEP DRAWDOWN

Lucky Peak is typically drawn-down around 20 feet in August as a way to manage water for the next irrigation season. In 2021, because of prolonged drought conditions, the drawdown was started a couple weeks earlier than normal and by the end of August Lucky Peak was 75 feet lower than usual. This drawdown resulted in the warmer surface water entering the outlet-zone which resulted in water temps being released from Lucky Peak that were 67 degrees all day long with water temperatures downstream at Glenwood Bridge reaching the low 70s. (Water temperature data was obtained from a public records request from the City of Boise who has a temperature logger just below Lucky Peak dam. Click on the graph to see a larger version.)

Looking back at Lucky Peak Reservoir elevation data, there has never been a drawdown in August like this. This year’s draw down is likely to impact Boise River water temperatures even more than 2021, because the reservoir level will drop another 33 feet than it did in 2021 (down 108 feet from 2020!), which will increase the percentage of outflows that are the warmer surface layer. There is no way to know how warm Lucky Peak’s outflow water temperatures will get, but it is possible they will reach the lower 70s, which means water temperatures at Glenwood bridge would warm into the mid 70s. 

High water temperatures are hard on trout, especially when the temperatures don’t drop below 65 degrees overnight for trout the bleed off the excess heat their bodies gained. Sadly, once Lucky Peak starts putting out water temperatures over 66 degrees in mid-August, this condition will exist on the entire river. Trout will seek out cool water refuge zones near ground springs and deeper holes, but will become overwhelmed by the prolonged high water temperatures.

IDAHO FISH AND GAME

If this condition happened in any of our neighboring states, their Fish/Game/Wildlife departments would issue a public warning and put short term restrictions on fishing—from a Hoot Owl warning to restrict fishing to just the morning hours to closing the fishery until water temperatures dropped.

However, Idaho Fish and Game takes a different approach to warm water conditions. They did a study on the Big Wood river and found that trout were much less likely to be caught in warmer water conditions. And although they found that those fish that were caught experienced a very high mortality rate they state that in the following years the fishery recovered. Because of this, they do not feel it is needed to close a river due to warm water conditions. You can read more about IDF&G’s position on this topic in this article: Perspective: Trout fishing during low water and high temperatures.

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While IDFG's study shows the trout population will rebound, there is no denying there will be short term impacts. And just like good C&R practices, avoiding fishing when water is too warm will maintain or improve fishing this Fall/Winter/Spring.

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A PERSONAL DECISION

I don’t disagree with IDF&G’s findings, nor do I want to start a debate about it. But I do think it is worth anglers thinking about it before they head out fishing. While IDFG looks at the whole fish population, anglers only have control over their own catch. My personal position is that if you believe that Catch and Release improves the fishing on a river, then you probably should avoid fishing waterways that are above 68 degrees. If you like fishing to keep your limit, then there is no reason to stop fishing. Keep in mind that fishing the Boise River through town is likely to be poor in these conditions, so it is smart to seek out cooler waters like the SF of the Boise River or the upper sections of the MF or SF Boise River. And if you do decide to fish the Boise in town this August, you should consider keeping what you catch, as they are unlikely to survive you are essentially wasting a gamefish.

Checking water temperatures before you go fishing is a good way to find the most productive water to fish. BVFF has water temperature gauges for local rivers on our Local Waters web page. It also helps to carry a stream thermometer. Fish Pond just came out with a new digital one that looks great! For more information on how to use a thermometer to improve your fishing, check out this previous Conservation Blog article.