Volunteers are not to conduct their normal sampling within one week of heavy rainfall (approximately more than 1 inch of rainfall in rural areas or ½ inch of rainfall in urban areas). During drought conditions, it is fine to monitor as long as water is flowing over riffles and is at least 3 inches deep. Do not monitor if water is standing or too low to flow. The best time to sample a stream is during its average conditions for that season. You can use the USGS stream gauge website as a guide.