The largest lake in the United Kingdom has turned into a "toilet," and the "catastrophe" is being "underestimated."

Loch Neagh, roughly the size of the Isle of Wight, provides water to 40% of Northern Ireland's population.

Some areas of Loch Neagh are covered in foam resembling mushy peas.

In reality, it is mushy peas that you've stored in the fridge for too long, and now it has spots of bright blue mold growing on it.

Recently listed for sale, a Los Angeles home priced at $4.25 million designed by Frank Lloyd Wright is "not for the faint-hearted."

The rest looks more like spotted green soup.

All of this is considered potentially lethal to domestic animals, livestock, and wildlife. In humans, it can cause stomach upset and skin rashes.

This is the largest lake in the United Kingdom, roughly the size of the Isle of Wight, supplying water to 40% of Northern Ireland's population.

Its vast scale and its impact on the environment, as well as fishing and recreation income, make this incident one of the largest pollution cases I have covered in 25 years.

James Orr of "Friends of the Earth" says the catastrophe is underestimated because it's not happening on the mainland.

"If this were happening in England, it would be such a big story that you couldn't get into the House of Commons; there would be so many outraged people outside."

This is a bloom of toxic cyanobacteria, known as blue-green algae. Satellite images clearly show pale green streaks across many miles of the surface.

The primary cause is the excrement of farm animals and, to a lesser extent, humans entering Loch Neagh.

This mixture of manure and urine is rich in phosphates, which provide nutrients and food for algae. Under certain conditions, such as the hot June and wet July of this year, the numbers spike sharply.

"Loch Neagh has become like a toilet," says Mr. Orr.

"It feeds the algae, and the algae, in turn, grow in such abundance, sucking oxygen out of the water and feeding to such an extent that it becomes a toxic soup."

Forty-one percent of Northern Ireland's territory drains into Loch Neagh, much of it agricultural land.

Over the past decade, there has been a targeted strategy for growing the agricultural economy: there are now many more intensive chicken producers, and the number of cattle and pigs has increased from 480,000 in 2013 to 738,000 in 2022.

Many campaigners and some scientists argue that the resulting pollution has been ignored. The Ulster Farmers' Union declined to be interviewed for our report, but farmers emphasize their key role in the economy, and other polluters, such as leaky septic tanks and wastewater treatment facilities, also feed the algae.

At the Agri-Food and Biosciences Institute (AFBI), work is underway to develop a solution that allows for high productivity with low pollution levels.

Dr. Gary Lyons of AFBI showed me the systems they are testing, which significantly compress digestate, extract liquid, and separate it into low-phosphate liquid fertilizer, while the drier fraction can be burned as biofuel. He says that if farms used such separators, the water would be much cleaner.

"We would see a massive reduction in the amount of phosphorus entering water bodies, and then a positive impact on water quality, and that's what we're looking for."

However, this technology costs thousands of dollars, and since new regulations do not require it, farmers are not expected to rush to adopt it.

Currently, there is no government administration in Northern Ireland that could set any new rules, as political disagreements stemming from post-Brexit trade agreements have paralyzed the Stormont Assembly.