Using new detection techniques, researchers have found trace amounts of various medicinal substances in lakes and rivers  Taken in large quantities, these substances could have serious health effects, but they are present in quantities far too low to cause any physiological response in people who drink the water or bathe in it
Nevertheless, medical experts contend that eliminating these trace amounts from the water will have public health benefits, since
some of the medicinal substances found in lakes and rivers are harmless to humans even if taken in large quantities