The USGS now has a text message and e-mail alerting system for their river gauges. It is available at: http://water.usgs.gov/wateralert/
The WaterAlert system allows you to subscribe to receive information about river gauge heights/flow rates. You can set parameters so that, for example, you can receive notification if a river gauge exceeds a specific gauge height/flow rate.
StreaMail allows you to send an e-mail or text message to email@example.com and it will immediately return the height/flow for the river that you specified.
This is a great tool if you live near a local river, as they tend to flood every once in a while.