 Hellbender populations were listed in 1981 as already extinct or endangered in Illinois, Indiana, Iowa, and Maryland, decreasing in Arkansas and Kentucky, and generally threatened as a species throughout their range by various human activities and developments.The hellbender salamander, considered a "habitat specialist", has adapted to fill a specific niche within a very specific environment, and is labeled as such "because its success is dependent on a constancy of dissolved oxygen, temperature and flow found in swift water areas", which in turn limits it to a narrow spectrum of stream/river choices.As a result of this specialization, hellbenders are generally found in areas with large, irregularly shaped, and intermittent rocks and swiftly moving water, while they tend to avoid wider, slow-moving waters with muddy banks and/or slab rock bottoms.