Habitat: North American Bullfrogs must live in water and are therefore usually found near some source of water, such as a lake, pond, or river. Warm, still, shallow waters are preferred. Bullfrogs are becoming increasingly common in areas that have been modified by humans. Increased water temperatures and increased aquatic vegetation, which are common factors of lakes polluted by humans, favor bullfrogs by providing suitable habitats for growth, reproduction, and escape from predators. Bullfrogs have a much higher critical thermal maximum than most other frogs, meaning that they are able to thrive in higher water temperatures. Bullfrogs have a longer breeding season and a higher rate of pre-metamorphic survivorship, which also allows them to be more successful than other frogs. Colorado, among many other places, is experiencing problems due to introduced bullfrog populations. Bullfrogs may have been introduced accidentally to trout streams and lakes during the Colorado Divisions of Wildlife fish stocking operations. Bullfrogs occasionally invade fish hatchery ponds and their larvae are caught along with the fishes routinely stocked in ponds and reservoirs. Most fish are averse to eating bullfrog tadpoles because of their undesirable taste.