You make a good point there Double Dry, I used to keep a log book, well sort of. After a while I just figured the times of day the diurnal swing was climbing and started to fish more through the swing. From a guiding stand point it makes sense but I dig getting to my spot early and just hanging out watching for bugs or fish activity. Nowadays I fish Spring Creeks more often and already know the temps are basically somewhere in the 50's year round.
This should be the map that covers the entire USA. Click on the State you want and it will pull up all the gauge locations. Then it takes a bit of 'searching' to find your particular stream/gauge. But if you just put the tip of the cursor on a dot it should tell you what/where, just not the actual information.
Edit: Took a bit of looking to find this one again.
SOOOOOOOO you know what's going on now in 'real time,' but what about tomorrow? This link gives you NOAA's best guess what the flows will be for the next few days. Same drill as above to pin down a given gauge.
Water temps may not deter one from pursuing warm water species. However, as has been mentioned playing salmonoids in water reaching 68 degrees is lethal. So, one should not practice catch and release fishing under this condition. Water temperatures do correlate with air temperatures. In the heat of the summer early morning fish can be safe on some trout and steelhead streams. Oregon's Deschutes river is a good example. Water temperatures are controlled at the Dams and are legally required to replicate historic flow temperatures. Warm water temperatures are at there highest at the beginning of the summer steelhead run. There is a mix of wild and hatchery fish at this time. All wild fish must be released unharmed. So, conscientious anglers do not fish until flows temperatures are dropped or only fish during the early morning hours. One could carry a thermometer. However, temperatures are posted online and are accurate and predictable. My partner and I also fish annually in Idaho and Montana. Our road trip includes a few tailwater fisheries and spring creeks. Favorable water temps can always be found with good planning, which is easy with the phone apps that are now available. The advantages of cell hones are now out weighing their minor annoyances. As I am driving, all my partner has to say is, Honey we are near some mountains now, I'm going to lose you, Goodbye... Then he checks on current condtions.
Location: White City (tad north of Medford) Oar-E-Gone
Re: How valuable is a thermometer?
+1 to what Dillon just posted. The maintain water temp is the 'Law of the Land' on the Rogue River. Rogue water comes out (like the Deschutes) from behind a very large dam at RM 157. Dam guys watch the water temps on the Rogue's gauges and iit's getting too warm; out goes more water from the bottom of the Lake.
Year round the water temp is not allowed to get much over 52 degrees in the upper river.
I like to try to fish ahead of the hatch. Meaning, that with temperature data I can fairly predict when a certain hatch may come off. It helps when rigging to know when to switch to a Blue Wing emerger pattern because the water temps are creeping one way or another and the BW's will begin to pop. This is especially helpful as seasons transistion and "new" hatches are beginning to appear.
I also use temps to gauge feeding behaviors on specific rivers I frequent. For the most part, I can predict when feeding picks up or drops because of temperatures. If we're not hitting fish, I'll know it's not because of temps. It's just another tool.
Couple this with flows, weather conditions, and reading the river, and you're ahead of the game. I've just given a couple examples of why I check water temps regularly, there are other reasons as well. I'm sure others will chime in.
PT, what decisions do you make based on the temp readings you take during the day?
I am more interested in bug activity, which determines, feeding activity of the Trout...as another poster has stated, temperature is an excellent precursor to stages of the hatch for most insects and the activity, along with light and air temps., for other biomass inhabitants . The thermometer also helps locate underwater seeps and springs, most helpful as the water heats up, in mid-summer, here in the West.
This is another nifty gadget that stays in the truck: