Maintaining a healthy population of any species can be challenging. Grizzly bears in Yellowstone National Park have been on the Endangered Species Act list since 1975 when the bear population reached a low of 136 bears. With the population now above 700 bears, the US Fish and Wildlife service is considering removing them from the list but maintaining a conservation plan and monitoring bear numbers. Views among environmental organizations differ, mostly because of concerns about the effectiveness of any conservation plan.