Ecological Disaster on the Wye

The water of the River Wye looks fine where it passes through Hay, and I've been enjoying going down to the bridge to spot fish in the water - but that's not the case elsewhere on the river, as reported in the Brecon and Radnor Express. There are places where the River Wye looks like thick green soup because of algal blooms.
The algae kills the aquatic plants that provide habitat for fish and other species, including birds, and reduces the amount of oxygen in the water. Combined with the recent high temperatures, that can kill a variety of fish.
The cause of the algal blooms appears to be extra phosphate in the water. Phosphate is used as fertiliser on farms - but it also comes from chicken manure, and since 2008 farmers have increased the numbers of chickens they keep in the catchment area of just one of the Wye's tributaries by an extra ten million. The amount of phosphate in the river has doubled in the last six years, and the river is now above the permitted levels under the EU Habitats Directive. One of the areas of concern is the catchment area of the River Lugg, which feeds into the Wye.
Locally over the last few years there have been protests about the erection of new chicken sheds on farms in the area, and it seems that Powys County Council have not been considering the cumulative effect when they have granted planning applications.
It's not just the Wye, either - other rivers in South Wales like the Usk are also affected by agricultural intensification. In 2018 the organisation Afonydd Cymru lodged a formal complaint with the European Commission about the lack of regulation in Wales, inappropriate planning and lack of Water Protection Zones.
The river is also a Special Area of Conservation under EU law and an Area of Outstanding Beauty, with two Sites of Special Scientific Interest along its length, one of them covering the upper Wye from Hay. In Radnorshire, it is also part of an Environmentally Sensitive Area - and even with all these legislative protections, it is not safe. And after all the floods of the winter which presumably flushed out any pollution, the levels of phosphate that are now causing the algal blooms must have come into the river since the floods went down.
The spokesman for Powys County Council in the Brecon and Radnor Express article said that the council assesses the planning applications carefully - but if that's the case, why have the phosphate levels in the river risen so fast? The River Wye is one of the most beautiful rivers in the UK, and used to be one of the cleanest - that's no longer the case.