Llyn Bodgynydd (Bod Mawr)

The chop figure here is modelled from forecast wind speed alone. It is not a measurement of the lake, and it does not account for fetch (the distance wind travels over water), lake size or shelter — so a long, exposed lake will be choppier than the figure suggests, and a small sheltered one calmer.

Fetch is the distance wind travels over open water. Longer fetch means more wave energy builds up. Shorelines on the windward side (where wind is blowing from) are typically calmer than leeward sides.

Good (green) means calm surface conditions suitable for most swimmers. Moderate (amber) means choppier water that may challenge some swimmers. Poor (red) means rough conditions not recommended for most people. Always assess the water yourself before entering.

The forecast shows expected surface state (from glassy to rough) and wind speed for each day, colour-coded good/moderate/poor. Use it to choose your best day, but always check current conditions on arrival.

Blue-green algae (cyanobacteria) can produce toxins harmful to swimmers. Live algae data is not shown on this page. Always check Environment Agency and local authority advisories before swimming, and avoid water that looks green or blue-green, has surface scum, or smells musty.