I'm surprised how many people still call our fly shop to get information about our local streams' water levels. Most of these people have never heard of the online USGS (United State Geological Survey) gauges that are available to everyone for free. There isn't a gauge for every stream, but there is one for most of the well known fly fishing destinations. The gauges show a stream's height in feet and its flow (discharge) in cfs (cubic feet per second). You can also find a stream's long term median flow and compare it to its discharge to see if the water is high, low, or right about average. Water temperatures are listed for a few streams but not for most of them. At the top of the page, you will see a drop-down box called "Geographic Area." You can use this box to check the flows of various streams and rivers for any state in the country. This site is an amazingly important resource, and I check it every day. You should too. Here's the link:
It's currently on the Pennsylvania page because that's where I keep it set in my favorites (after all, I do live in PA). But again, just toggle through it to find the water you plan to fish this week. It just may save the day for your next trip. Good luck!