Water testing results for the River Corran and Mackerel Lake Stream. October 2026

Here is our monthly water report update from the Laugharne Citizen Science Group for October 2026! By comparing October’s results against our year-round data, we get a clear picture of how autumn rain, agricultural run-off, and seasonal changes are impacting our aquatic ecosystems.

River Coran (Abercorran to Newbridge)

The overall picture along the main part of the River Coran this October shows stable water clarity, good oxygenation, and a welcome recovery in pH levels, but persistent challenges remain with nutrient pollution—particularly nitrates and phosphates.

1. Welcome pH Recovery Across the Catchment

During late summer, our monitoring recorded worrying drops into acidic pH conditions. We are pleased to report that in October, pH levels across all testing locations (from Abercorran downstream to Newbridge Road Bridge) have fully rebounded to healthy, slightly alkaline levels (ranging between 8.1 and 8.6). This creates a much safer, balanced environment for local fish species, invertebrates, and plant life.

2. Chronic Nitrate Levels Across the Reach

Nitrates continue to be one of the main ecological concerns for the Coran. According to UK river health standards, unpolluted natural rivers should ideally have nitrate levels below 1.0 mg/L, with anything over 5.0 mg/L considered excessive. In October, elevated levels were recorded along the reach: starting at Abercorran with an excessive peak (5.8 mg/L), and measuring 2.0 mg/L further downstream at Newbridge Road Bridge. Autumn rainfall washing agricultural nutrients from surrounding land into the river continues to drive these elevated figures.

3. Localized Phosphate Spike at Glancorran

While most Coran monitoring points held steady moderate phosphate levels (0.11–0.19 mg/L), Glancorran experienced a noticeable surge up to 0.37 mg/L this month (nearly four times its September level). Phosphate readings above 0.30 mg/L enter a high-risk zone that can trigger excessive algal growth and disrupt river ecology.

Mackerel Lake Stream & Culvert

Smaller watercourses and streams feeding into the catchment react quickly to weather conditions and localized inputs. In October, testing at Culvert revealed a key finding:

Major Phosphate Concentration at Culvert

The stand-out finding in this month's testing is a sharp increase in phosphates at Culvert, reaching 0.59 mg/L. This is nearly double September's reading (0.30 mg/L) and represents the highest phosphate reading recorded at this site all year. Elevated phosphates in small tributaries are typically linked to autumn field run-off or domestic wastewater inputs. On a positive note, ammonia levels at Culvert remained virtually zero (0.00 mg/L), showing no evidence of fresh organic sewage contamination.