River Corran and Mackerel Lake stream water testing-September 2026

Catchment Monitoring :Monthly Comparative Analysis | River Corran & Mackerel Lake

Stream

1. Mackerel Lake Stream Catchment

This catchment covers Llandawke, Broadway Caravan Park, and the Culvert bypass. Due to dry conditions, Llandawke had no water and remained unsampled in September.

Ammonia (Good): Broadway Caravan Park registered 0.22 mg/L (up from 0.02 mg/L in August), while the Culvert remained at 0.00 mg/L. Although Broadway experienced an increase, it remains below the 0.3 mg/L threshold considered ecologically good.

Nitrate (Low / Elevated): Broadway Caravan Park recorded 0.0 mg/L (this reading was verified with 3 separate re-tests to confirm accuracy, down from 1.3 mg/L in August). The Culvert measured 1.7 mg/L (down from 2.1 mg/L in August), continuing in the elevated range (1.0 – 4.9 mg/L) but well below excessive levels.

Phosphate (High / Upper Medium): Broadway Caravan Park rose to 0.455 mg/L (up from 0.30 mg/L in August), placing it firmly into the High phosphate category (0.3 mg/L). The Culvert increased to 0.300 mg/L (up from 0.19 mg/L in August), reaching the boundary of the High tier.

2. Main River Corran Catchment

This section evaluates the primary river sampling stations: Abercorran, Glancorran, Horsepool Tributary, Hill Farm Stables, Horsepool Road Bridge, and Newbridge Road Bridge.

pH Balance (Critical Acidic Dip at Abercorran)

Abercorran experienced a sharp drop in pH down to 4.5 (falling from 8.5 in August). This falls below the critical 5.0 threshold where fish mortalities can occur.

Important Sampling Context (Abercorran pH): Sampling at Abercorran occurred during near-dry, low-water conditions where water was reduced to a small, stagnant pool. In minimal water volumes, localized organic decomposition and loss of stream flow significantly reduce buffering capacity, leading to localized acidic spikes. It will be interesting to see how these readings compare with October when the river begins to flow again

This reading reflects localized pool stagnation rather than the chemical baseline of the wider flowing river.

The remaining sampled river stations also shifted towards the lower boundary of the acceptable range (6.0 –

9.0): Glancorran (6.0), Horsepool Road Bridge (6.0), Horsepool Tributary (6.1), and Hill Farm Stables (6.2).Newbridge Road Bridge was not sampled for pH in September.

Nitrate Trends

Abercorran: Spiked back into the excessive category at 5.5 mg/L (up from 3.9 mg/L in August).

Glancorran: Dropped to 4.1 mg/L (down from 5.3 mg/L in August), returning to the elevated tier (1.0 – 4.9 mg/L).

Other River Sites: Horsepool Rd Bridge (3.4 mg/L), Horsepool Tributary (3.1 mg/L), Newbridge Rd Bridge(3.0 mg/L), and Hill Farm Stables (2.7 mg/L) all stayed within elevated boundaries.

Phosphate: Horsepool Rd Bridge spiked to 0.330 mg/L (up from 0.23 mg/L in August), crossing into the High category (0.3 mg/L). Newbridge Rd Bridge (0.270 mg/L) and Abercorran (0.250 mg/L) sit near the top of the medium range, while Hill Farm Stables (0.170 mg/L), Horsepool Tributary (0.160 mg/L), and Glancorran (0.100 mg/L) remain in the medium tier.

Salinity: Salinity at Abercorran returned to a normal baseline of 0.16 (down from the August peak of 0.80).

Other sites recorded low values between 0.09 and 0.12.

Ammonia (Pristine): Background ammonia remained excellent across the river, with 0.00 mg/L recorded at almost all sites except for a trace reading of 0.04 mg/L at Newbridge Rd Bridge.

Water Temperature: General autumn cooling was evident along the main channel, with water

temperatures ranging between 13.6°C (Abercorran) and 14.8°C (Glancorran). Newbridge Road Bridge recorded a higher water temperature of 17.5°C.

Dissolved Oxygen Note: Dissolved Oxygen testing was suspended for September due to an equipment meter malfunction.