April. Testing results for the River Corran and Mackerel Lake stream

Spring River Health Report (April 2026): Tracking the "Invisible" Surge

In April 2026, the monthly monitoring has revealed a significant trend across the catchment. While our rivers appear visually clear and healthy, the chemical data reveals a hidden "nutrient surge" that is affecting the river’s ecology.

The Post-January Loading Phase

Under current Welsh regulations (CoAPR), the closed period for slurry spreading ended on January 15th. Since then, there have been three months of active land management across the West Wales "Dairy Belt." Our latest data shows Nitrate (NO3) levels reaching "excessive" concentrations in the river Corran, peaking at 7.90 mg/L (GlanCorran) and 6.20 mg/L (AberCorran).

What is notable this month is the absence of visible slurry. Because Ammonia (NH3) remains at zero, we know we are not looking at a fresh surface spill. Instead, we are potentially witnessing the result of groundwater leaching.

The Role of Shale and Soil

The local landscape is characterised by loamy soils sitting atop sandstone bedrock.That confirms the sub-surface leaching theory. In a "shaly" environment (typical of the Silurian and Ordovician mudstones of West Wales with Old Devonian Sandstone nearer the coast), the river isn't just being fed by surface runoff; it is being fed by the water table.

The bedrock acts like a series of pipes. When slurry is spread after the January 15th deadline, the liquid nitrogen soaks through the shallow topsoil and enters the fractures in the shale. By the time that water "bleeds" out into the river in April, the solids and the smell have been filtered out by the earth, but the Nitrates remain dissolved in the water.

This explains the "invisible" results perfectly: High Nitrates, High pH, but crystal-clear water. When slurry is spread, the nutrients soak into the ground and travel through the cracks in the rock. By the time this water reaches the river, the organic solids have been filtered out, but the dissolved nitrates remain. This creates a "hidden" pollution source that bypasses surface detection but remains highly impactful to the river's chemistry.

The pH Spike: A River in Overdrive

The most striking trend in April is the sharp rise in pH, with several sites hitting 8.9—dangerously close to the threshold for aquatic stress. Without visible pollution to blame, this rise is driven by a biological "sugar high."

These high nitrate levels act as a potent liquid fertiliser. Even in clear water, microscopic algae and diatoms(Diatoms are a major group of algae and are among the most common types of phytoplankton found in both freshwater and saltwater. In the Corran river system, they are likely the "invisible engine" driving those high pH and DO readings seen in the April figures.) are currently undergoing an explosive growth spurt furled by increasing spring sunlight. As they photosynthesise, they strip Carbon Dioxide (CO2)—a natural acid—out of the water. With the acid removed, the river’s pH climbs. This "invisible bloom" is a warning sign that the river is becoming over-productive.

The "Safety Net" of Cold Water

Currently, our Dissolved Oxygen (DO) levels remain very healthy, averaging 10.5 mg/L. April’s cool water temperatures (12.5°C–13.5°C) allow the water to hold high concentrations of oxygen, protecting fish and macro-invertebrates for now. However, this is a temporary grace period.

Looking Ahead: The Summer Transition

As we head into May and June, we expect this "invisible" loading to manifest in visible ways. As temperatures rise, these high nitrates will likely trigger an explosion of blanket weed and algae. While the water looks healthy today, the chemistry tells us the river is "fully loaded" for a challenging summer. We will continue our monthly monitoring to track this transition as the growing season accelerates.