A report concludes that blooms of toxic cyanobacteria, or blue-green algae, are a poorly monitored and underappreciated risk to recreational and drinking water quality in the United States, and may increasingly pose a global health threat. Several factors are contributing to the concern. Temperatures and carbon dioxide levels have risen, many rivers have been dammed worldwide, and wastewater nutrients or agricultural fertilizers in various situations can cause problems in rivers, lakes and reservoirs. No testing for cyanobacteria is mandated by state or federal drinking water regulators, according to scientists from Oregon State University, nor is reporting required of disease outbreaks associated with algal blooms. But changes in climate and land use, and even increasing toxicity of the bacteria themselves, may force greater attention to this issue in the future, the researchers said.