Streamside thermometer. I keep losing them so I bought another one today. Checking temps and self regulating your time on the water might be the most important thing you can do for the fish. Don't wait for the agencies to close the water, they lag.
I can't remember when the ODF&W ever closed down a fishery due to water temp. I'm not sure they have.
When the lakes and reservoirs become very, very low, normally they just remove the limit on the trout so anglers can keep as many as they want.
I remember one low water year when all the trout in Crane Prairie were located in one specific spot and that spot was surrounded by fishing boats. The department should have closed the reservoir to fishing but instead simply removed the limit restriction. Crazy solution but that's how they operate.
Over the years I had lost a number of thermometers which were encased in a metal tube. Either the cap unscrewed, or the cheap bail let go and it went into the water. I have since learned my lesson and add locktite to the threaded cap and changed out the cheap ring with a key ring type holder and connect it to a lanyard. I have not lost one since making the upgrades.
Ball point pen. Now that we have "mandatory retention" of hatchery steelhead on rivers tributary to the Columbia River, a writing implement is necessary to promptly record a steelhead on my catch record card immediately upon reducing that slime rocket to possession.
Stream thermometer is nice. Water was a comfy 54.4*F yesterday; I wouldn't have wanted to be wading wet, especially crotch deep or deeper. I envy Swimmy's infrared thermometer tho, and to think I thought my Orvis digital stream thermometer was the shizzle, but so old school now.
Yes on many waters. . 3 wks ago I quit a lake that hit 71. Had a fish belly up after release. Heading to GT in the next few days to scout in advance of Youth Camp which starts on the 12th. I wish I was in the Yellowstone area. 3-4 hrs floating on Hebgan is hard to beat. Daytime temps 80s nighttime mid 40s.