Frog population changes in North America with different limb, 20-30%, people would worry such species may affect and post risk to people in the local area cause their drinking water is from the river.The U.S. Geological Survey study, released Wednesday, is the first to document how quickly amphibians are disappearing, as well as how low the populations of the threatened species could go, given current trends. The exact reasons for the decline in amphibians, first noticed decades ago, remain unclear. But scientists believe several factors, including disease, an explosion of invasive species, climate change and pesticide use are contributing. The study said the populations of seven species of threatened frogs, including the boreal toad and the yellow-legged frog, are decreasing at a rate of 11.6 percent a year. More than 40 species of frogs, such as the Fowler’s toad and spring peepers, are declining at a rate of 2.7 percent. If that pace keeps up, their populations will be halved in 27 years, the study said.