Before beavers were extirpated world-wide, hundreds of dams in the headwaters of major rivers moderated their flows. Instead of water running downstream in hours, a typical leaky beaver dam may slow this to days or weeks. Keeping water on the land longer, means that more of this important resource is available for animals and humans. Taxpayers need not pay for increasingly large culverts and bridges downstream to accommodate the flow when many beaver impoundments upstream are regulating the flow. Dams, which cause small, localized flooding, play an important role in controlling regional floods when they are numerous in the headwaters of a watershed. As the quantity and quality of water suppiies becomes more critical, both within countries and internationally, recognition of the beaver’s key role is growing.