Prague, Czech Republic — Beavers have saved Czech taxpayers a cool $1 million by flooding a protected former army training site where a long-stalled dam was planned, a conservation official said on Tuesday.

Among nature's great engineers, beavers and their inventions have long been championed by environmentalists for their ability to protect against flooding, improve water quality, and boost wildlife.

Officials had hoped to build a barrier to shield the Klabava River and its population of critically endangered crayfish from sediment and acidic water spilling over from two nearby ponds.

As a bonus it would turn a part of this protected area south of the capital Prague into a nature-rich wetland.

First drafted in 2018, the project had a building permit but was delayed by negotiations over the land, long used by the military as training grounds.

Yet before the excavators got the green light to begin digging, the herbivorous rodents set to work building a dam of their own.

"They built a wetland with pools and canals," Bohumil Fiser from the Czech Nature Conservation Agency told AFP.

"The area is roughly twice larger than planned."

'Full service'

The beaver family then moved on to a gulley encircling the ponds, in which the conservationists wanted to build little dams to allow overspill that would help flood the area.

So far the beavers have built at least four dams in the gulley and are currently working on more.

"We were only discussing (building the dams in the gulleys) with the water company and the forest company which owns the land," said Fiser, who manages the area.

Fiser said the estimated savings to the Czech purse reached some 30 million Czech koruna ($1.2 million).

"It's full service, beavers are absolutely fantastic and when they are in an area where they can't cause damage, they do a brilliant job," he said.

Despite the good beavers do to the land around them the furry mammals have their critics, with farmers and others complaining of the destruction they cause by felling trees.

But any farmers whose land could be at risk are located far from the site, which was declared a protected area in 2016.

"We don't expect any conflict with the beaver in the next 10 years," Fiser added.