06/04/2026
35% of the World's Wetlands Have Been Lost Since 1970. The Beaver — the Animal That Creates and Maintains Wetland Ecosystems — Was Eliminated From Most of Europe and 90% of North America by the 19th Century. The Ecosystems Left With Them.
Drain the beaver. The wetland goes. The wetland goes — and 35 species go with it.
The North American Beaver (Castor canadensis) and the Eurasian Beaver (Castor fiber) are the world's second-largest rodent (after the Capybara) and the only non-human animal that substantially modifies its own habitat to create the environment it needs — a behaviour called ecosystem engineering.
A beaver dam transforms a stream section into a pond. The pond:
— Raises the water table of surrounding land, maintaining moisture in adjacent meadows and forest during dry periods
— Creates standing water habitat for amphibians, fish (beaver ponds are among the most productive freshwater fish nursery habitats in both North America and Europe), birds, and invertebrates
— Traps sediment and nutrients from upstream, reducing downstream silting
— Slows flash flood events by holding water in ponds upstream
The North American Beaver was reduced from an estimated 60–400 million individuals to approximately 100,000 by the 1900s through the fur trade. The Eurasian Beaver: reduced to fewer than 1,200 individuals in isolated fragments by the early 20th century from hunting for fur, castoreum (a gland secretion), and perceived agricultural conflict.
When the beavers went: the wetlands they maintained degraded. Streams returned to faster-flowing, drier channels. The water table dropped. The amphibian populations that depended on beaver ponds collapsed.
Reintroduction results: where beavers have been reintroduced in Britain (River Otter, Devon; River Tay, Scotland) and the US, documented recovery of amphibian populations, fish communities, and water table levels within 5–10 years.
When removing one animal can collapse a wetland ecosystem — and reintroducing that animal can restore it within a decade — does that change how we categorise the beaver: as a rodent, or as infrastructure?
