Prior posts have noted the Gulf of Mexico/Carribean dead zone at the mouth of the Mississippi River Delta. Prior posts have discussed in detail the cause for such blooms, the overuse of nitrogen and phosphorus fertilizers by agricultural operations and the discharge of nitrogen and phosphorus wastes from sewage treatment plants. Such adverse impacts are being seen not only in other U.S. locales, but worldwide. See, for example, http://www.usgs.gov/blogs/features/usgs_top_story/dead-zone-the-source-of-the-gulf-of-mexicos-hypoxia/ and http://www.cep.unep.org/publications-and-resources/marine-and-coastal-issues-links/nutrients.
Recently, the City of Toledo was much in the news because toxic algae blooms, driven by the same nutrients (which are usually key to all such blooms), were proving hazardous to drinking water supplies. Ironically, EPA does not require testing for such toxins, but the City fortunately had its own testing program. See, for example, http://www.poughkeepsiejournal.com/story/tech/science/environment/2014/08/17/toxic-algae-can-put-water-sources-risk/14061669/ and http://www.usatoday.com/story/news/nation-now/2014/08/04/toledo-ohio-water-toxin-explainer/13563805/.
But, the problem is more widespread. The Shenandoah Riverkeeper has apparently be working with the Virginia DEQ and U.S. EPA to recognize and regulate such blooms in the Shenandoah River. Because Riverkeeper views voluntary action as insufficient, it has filed a notice of intent to bring an action under the CWA. See http://www.potomacriverkeeper.org/updates/shenandoah-riverkeeper-files-notice-intent-sue-epa-failure-address-algae-shenandoah-river.
Given the known potential for harm from such blooms, and given that the cause is widely understood, it would appear prudent for water providers (even when not required to do so by Federal or State regulation) to implement voluntary monitoring programs.