1 gauge, at Peblic Seiont River Station. It is not above its typical high. 2 storm overflows upstream are discharging now. Gauges in Gwynedd; levels are checked every 15 minutes.
Stations are listed from source to mouth as the water flows, traced on the river map (OS Open Rivers) and the Environment Agency’s own links between its gauges. A distance “by river” is along the river, and is shown only where the map traces the path.
Streams and rivers with a gauge whose water joins the Seiont above one of its gauges, from the source down. The river map knows where gauges are, not every stream, so a tributary without a gauge is not listed here.
8 storm overflows are traced upstream of Peblic Seiont River Station, the Seiont’s lowest gauge on the river map: on the Seiont itself, on its gauged tributaries, and on smaller streams that join above there.
2 report discharging now
6 not discharging
0 offline or silent: 0 monitor offline, 0 status unknown, 0 no live feed
Official figures for 2025, for the overflows traced upstream of Peblic Seiont River Station: 672 spills over 5,732 hours in total, across all 8.
Each overflow is listed in the stretch above the first gauge its water reaches, from the source down, as on the Gauges tab. A stretch of the Seiont includes the smaller streams that join it there.
Above Peblic Seiont River Station, the Seiont’s highest gauge8 overflows · 2 discharging now
Dôl Eilian Llanberis Storm OverflowNot discharging Dwr Cymru Welsh Water · into Afon Hwch · 14.2 km by river above Peblic Seiont River Station · 2025: 45 spills, 105 h
Llanberis WwTW Storm OverflowDischarging now since bathing water Dwr Cymru Welsh Water · into Afon Y Bala · 13.4 km by river above Peblic Seiont River Station · 2025: 137 spills, 1,196 h
Llanberis Maes Padarn Storm OverflowNot dischargingbathing water Dwr Cymru Welsh Water · into Goch Bach · 13.3 km by river above Peblic Seiont River Station · 2025: 50 spills, 266 h
Clwt-Y-Bont Storm OverflowNot discharging Dwr Cymru Welsh Water · into Afon Caledffrwd · 11.3 km by river above Peblic Seiont River Station · 2025: 4 spills, 3.8 h
Stad Hafod Deiniolen Storm OverflowNot discharging Dwr Cymru Welsh Water · into Afon Caledffrwd · 11.2 km by river above Peblic Seiont River Station · 2025: 129 spills, 630 h
Brynrefail Main Storm OverflowNot discharging Dwr Cymru Welsh Water · into Afon Caledffrwd · 9.5 km by river above Peblic Seiont River Station · 2025: 52 spills, 296 h
Station Road Pontrhythallt Storm OverflowNot discharging Dwr Cymru Welsh Water · into River Seiont · 7.3 km by river above Peblic Seiont River Station · 2025: 140 spills, 1,381 h
Llanrug WwTW Storm OverflowDischarging now since Dwr Cymru Welsh Water · into Afon Seiont · 5.8 km by river above Peblic Seiont River Station · 2025: 115 spills, 1,855 h
Near these gauges, connection not known
Within 3 km of one of the Seiont’s gauges in a straight line, but the river map cannot say whether their water reaches it.
Crown Street Caernarfon OverflowNot discharging Dwr Cymru Welsh Water · into Menai Strait · 1.8 km from Peblic Seiont River Station in a straight line · discharges to the sea, an estuary or tidal water · 2025: 0 spills, 0 h
Castle Ditch Storm OverflowNot discharging Dwr Cymru Welsh Water · into Afon Seiont · 1.9 km from Peblic Seiont River Station in a straight line · discharges into a tidal reach, where the water moves both ways · 2025: 0 spills, 0 h
Bank Quay Caernarfon Storm OverflowNot discharging Dwr Cymru Welsh Water · into Menai Strait · 2.0 km from Peblic Seiont River Station in a straight line · discharges to the sea, an estuary or tidal water · 2025: 0 spills, 0 h
Balaclava Road Caernarfon Storm OverflowNot discharging Dwr Cymru Welsh Water · into Menai Strait · 2.0 km from Peblic Seiont River Station in a straight line · discharges to the sea, an estuary or tidal water · 2025: 1 spill, 0.3 h
B4419 Caernarfon Storm OverflowNot discharging Dwr Cymru Welsh Water · into Menai Strait · 2.0 km from Peblic Seiont River Station in a straight line · discharges to the sea, an estuary or tidal water · 2025: 67 spills, 96 h
Waterloo Port Road Storm OverflowNot discharging Dwr Cymru Welsh Water · into Menai Strait · 2.1 km from Peblic Seiont River Station in a straight line · discharges to the sea, an estuary or tidal water · 2025: 0 spills, 0 h
11 other overflows within 3 km of these gauges are placed below the Seiont’s lowest gauge or on another river, so not listed.