Wales · Cardiff
Llanishen Reservoir
Caution. Sewage discharge 2.4km away 2 days ago.
Water quality only This says nothing about tides, rip currents, cold water shock or lifeguard cover. Cold water and currents are dangerous even when the water is clean. Read the local signs before you go in. What we cannot tell you.
Checked UK time
Why this verdict
- Bathing season
- Closed until 15 May (neutral factor)
- Discharge nearby
- 2.4km 2 days ago (negative factor)
- Annual classification
- Excellent (positive factor)
- Latest E. coli
- 10 cfu/100ml (positive factor)
- Latest intestinal enterococci
- 10 cfu/100ml (positive factor)
Out of season
Weekly sampling and the daily pollution-risk forecast pause on 30 September and resume on 15 May. This verdict rests on the annual classification, live storm-overflow data and rainfall in the last 24 hours.
Storm overflows are driven by rain, so they spill more in autumn and winter than in summer. See every spill happening now across the UK.
Recent sewage discharges nearby
Storm overflows operated by Welsh Water within ten kilometres in the last 48 hours.
- Ended 2 days agoHeathwood Road Storm Overflow · into Nant Y Wedal2.4km from the bathing water
- Ended 2 days agoBall Lane Storm Overflow · into River Rhymni3.0km from the bathing water
- Ended 2 days agoBegan Road Cardiff Storm Overflow No2 · into River Rhymni3.8km from the bathing water
- Ended 19 hours agoBedwas Road Storm Overflow · into Porset Brook6.0km from the bathing water
- Ended 2 days agoPentwyngwyn Road Storm Overflow · into River Rhymney6.3km from the bathing water
- Ended 2 days agoCardiff Eastern Short Sea Outfall Storm Overflow · into Severn Estuary6.4km from the bathing water
- Ended yesterdayPlas Machen Storm Overflow · into River Rhymni6.8km from the bathing water
- Ended 2 days agoTrelai Park Storm Overflow · into River Ely6.9km from the bathing water
- Ended yesterdayMachen Close St Mellons Storm Overflow · into Severn Estuary7.5km from the bathing water
- Ended 2 days agoHarrowby Street Storm Overflow · into River Taff Estuary7.6km from the bathing water
- Ended 2 days agoGrangetown Storm Overflow · into River Taff7.8km from the bathing water
- Ended 19 hours agoRhydlafar WwTW Storm Overflow · into Nant Dowlais8.0km from the bathing water
- Ended 2 days agoPenarth Road Storm Overflow · into River Ely8.6km from the bathing water
- Ended 2 days agoGraig-Y-Fedw Storm Overflow · into Nant Yr Aber9.2km from the bathing water
- Ended 2 days agoPenarth Head Storm Overflow · into Severn Estuary9.8km from the bathing water
- Ended 19 hours agoTonteg Road Taff Vale Storm Overflow · into River Taff9.9km from the bathing water
See Welsh Water's own storm-overflow map(opens in a new tab) →
Latest bacteria reading
Latest sample · 9 September 2026 · 3 weeks ago
- E. coli
- 10cfu/100ml
- Intestinal enterococci
- 10cfu/100ml
This is the most recent reading. Sampling resumes on 15 May. E. coli and intestinal enterococci are the indicator organisms used in the official classification.
Common questions
- Can you swim at Llanishen Reservoir?
- Caution. Sewage discharge 2.4km away 2 days ago. Llanishen Reservoir is a designated bathing water, so it is sampled and rated every season. This answer covers water quality only, not tides, currents or lifeguard cover.
- What is the water quality like at Llanishen Reservoir?
- Llanishen Reservoir is rated Excellent in the regulator's 2025 annual classification, a percentile taken over readings from up to four bathing seasons. The most recent sample, taken 9 September 2026, showed 10 cfu/100ml of E. coli and 10 cfu/100ml of intestinal enterococci.
- Has there been sewage at Llanishen Reservoir recently?
- Yes. 16 storm overflows within ten kilometres of Llanishen Reservoir: 16 in the last 48 hours.
Where this data comes from
- Contains Natural Resources Wales information © NRW and database right
- Contains water-company storm overflow data, licensed under OGL v3
- View the regulator's full profile
Other beaches nearby
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Gareth Clubb