Fish and wildlife could die after criminals destroyed a machine controlling algae levels, the month after it was installed.

The £25,000 ultrasound unit, that was fitted in the Rickmansworth Aquadrome in July, was vandalised on August 14.

Sharp instruments were used to cut wires attaching the unit to a buoy in Batchworth Lake. The doors had been prised off and wires inside the machine were also severed.

If blue-green algae blooms in the lake, oxygen levels in the water would drop meaning fish could suffocate.

Three Rivers District Councillor Sarah Nelmes, who represents Penn and Mill End, said: “This could not have occurred accidentally and naturally I’m disappointed that one of the expensive units the council installed has been damaged in this way.

“The Aquadrome is a wonderful local asset where residents can enjoy nature and the environment, and we need the continued support of users to keep it that way.

“If levels of blue-green algae in the Aquadrome get too high, it can have a harmful effect on people, pets, plants and fish so the council has recently been using ultrasound to maintain algae at a healthy level.”

The council is hoping the machine can be repaired but do not know how much that will cost.

Algae has been a potential problem at the Aquadrome for a number of years. The ultrasound units were installed to prevent any risks to wildlife.

Hertfordshire Constabulary said they are treating this as criminal damage and urge anyone with information about the offenders to contact 101.