Warning about toxic green ‘mashed potato’ foam that can kill dogs in just 24 HOURS: Pet owners have warned about toxic algae that is invading rivers, lakes and ponds and is deadly to animals

Experts are warning dog handlers about toxic algae that looks like “green mashed potatoes” and can be fatal if swallowed.

Blue-green algae spread in “blooms” over lakes and rivers, turning the water a bright green color and giving it an earthy or musty smell.

But the substance contains toxins that can affect a dog’s liver function and potentially cause death within an hour.

A woman tragically lost her beloved two-year-old pooch after it came into contact with the deadly substance at a lake in Somerset.

A hard-hit freshwater lake – Lough Neagh in Northern Ireland – is being devastated by the algae that have formed uncontrollable blooms over the summer.

An expert said the substance (pictured) could look like a “green, mashed potato-like crust.”

Harmful algae blooms have covered large parts of Northern Ireland’s Lough Neagh throughout the summer

It comes as environmentalists hold a memorial service at Lough Neagh to commemorate the famous lake’s alleged death from the substance officially known as cyanobacteria.

Lough Neagh, the largest freshwater lake in the United Kingdom or Ireland, supplies 40 percent of Northern Ireland’s drinking water and is the base of a large eel fishery.

Although ingestion of cyanobacteria is not known to be fatal to humans, it can lead to serious illnesses.

“The state of the lake is currently simply appalling,” said environmental scientist Dr. Leslie Gornall told BBC Radio 4 on Thursday.

“At the end of the lake there is a crust that looks like green mashed potatoes, at least 15cm deep and possibly 18cm deep.

“If you put the rudder of a boat in it, the full rudder blade can jump up and act like a shovel…it smells disgusting.”

Blue-green algae contains toxins that can kill livestock, wildlife and pets – both cats and dogs.

“If you let your dog in there to chase a ball, he’ll come out, lick his fur and then he’ll be dead in 24 hours,” Dr. Gornall.

“Immediate action is needed otherwise we will not only lose the lake but the Lough Neagh eel will become extinct… and we will lose tourism too.”

Lough Neagh supplies 40 percent of Northern Ireland’s drinking water and is home to a large eel fishery, but is devastated by the algae

Algae on the surface of Lough Neagh as environmental activists hold a wake to protest the lack of action

An adorable two-year-old flat-coated retriever named Cove (pictured) died less than 45 minutes after being poisoned by blue-green algae in Somerset

Blue-green algae is by no means unique to Lough Neagh, and the substance has recently been spotted in Lake Windermere in Cumbria, Highams Park Lake in London, the Jubilee River in Berkshire and Wimbleball Lake in Somerset.

An interactive map shows the locations of cyanobacteria in UK waters, as reported by members of the public.

Blooms make bodies of water look like pea soup or spilled green paint, but they can also look like more solid clumps or foam, especially near shore.

Some communities have posted signs warning of the dangers of poisoning a lake with the blooms. However, this is not always the case.

Dogs that run away from their owners while on leash could end up in an affected river or lake before the owner even notices.

A Blue Cross spokesman said there was no antidote to the toxins produced by the blue-green algae.

“If caught early enough, your veterinarian will likely try to get your dog sick and flush the toxins from the body before they take hold,” they said.

“Unfortunately, blue-green algae poisoning often leads to fatal liver failure.”

In humans, contact with blue-green algae can cause skin rashes, nausea, stomach pain, fever and headaches.

According to the Blue Cross, there have been some reports of more serious illnesses, including liver and brain damage, but there have been no confirmed human deaths.

Because of their comparatively lower body weight, children are at higher risk of developing problems than adults.

Affected waters at Frampton on Severn in Gloucestershire. Algae growth is related to an excess of nutrients in the water.

Sign at Preston Marina in Lancashire warning the public about the dangers of blue-green algae

Because of the health risks, anglers are urged not to eat anything they catch in waters they suspect are affected.

Although the cyanobacteria are not a new species, their growth in recent months has been fueled by the summer heat.

A combination of warm temperatures, sunlight and nutrient-rich water causes blue-green algae to multiply or “bloom” quickly.

Nitrogen and phosphorus from agricultural fertilizer runoff from fields is thought to be another important factor

The spread of the invasive zebra mussel species is also thought to have played a role, making the water clearer, allowing more sunlight to penetrate and stimulating photosynthesis.