Lac d'Isaby

Lac d'Isaby is a glacial mountain lake in the commune of Beaucens, in the Hautes-Pyrénées department of southwestern France. Sitting at roughly 1,589 metres above sea level, it covers an area of about 6.3 hectares and lies on the boundary between the Pic du Midi de Bigorre massif to the south and the Montaigu massif to the north. Beaucens is home to more than one small lake, including the separate and unrelated Lac d'Ourrec nearby, so it's worth keeping the names straight when planning a visit.

How did the lake form?

The basin was carved out by glacial and fluvioglacial erosion over thousands of years during the Pleistocene, when a cooling climate triggered the formation of glaciers across the Pyrenees. That long process left behind the lake's distinctive crescent shape, framed on all sides by high ridgelines.

How do you get to Lac d'Isaby?

The classic approach starts at the top of the Hautacam ski station, from which the trail heads downhill and partly follows the Isaby stream before reaching the lake. The round trip covers around 7 kilometres, is rated as a moderate walk, and typically takes two to three hours depending on pace and photo stops. Elevation change is modest, which makes the route manageable for families with children. To reach Hautacam, drivers follow the departmental road through Argelès-Gazost; the trip from Lourdes takes about 50 minutes by car. The best window for a visit runs from March through October, since the trail can stay snow-covered outside that period.

What will you see along the way?

The surroundings are classic high-mountain pasture: wide grazing meadows where cattle and sheep spend the summer, dotted with patches of wild blueberry bushes. Kestrels can often be spotted circling above the slopes, while the lake itself holds trout and small minnow-like fish. The payoff for hikers is a 360-degree panorama of the surrounding peaks, which is a big part of why this walk is one of the more popular outings around Argelès-Gazost.

A local legend

The lake is tied to an Occitan folk tale called Era Sèrp d'Isavit, about a giant serpent said to have once lived on the peaks above Argelès-Gazost, devouring cattle, sheep, dogs, and even shepherds. The story is still mentioned in local accounts of the area as a piece of regional folklore that accompanies the hike.

Rules to know before you go

The lake sits within the Pyrenees National Park, so a few conservation rules apply. Dogs are welcome but must stay on a leash. Swimming is discouraged, since it can disturb the lake's fragile aquatic ecosystem. Bivouac camping is tolerated only between 7 p.m. and 9 a.m., letting hikers spend a night under the stars without disrupting daytime park life.

Frequently asked questions

Where exactly is Lac d'Isaby located? In the commune of Beaucens, Hautes-Pyrénées, between the Pic du Midi de Bigorre and Montaigu massifs.

How long does the hike take? The standard round trip from the Hautacam ski station takes roughly two to three hours.

Is the trail suitable for families? Yes, it's generally rated moderate and manageable for families, though it's worth checking weather and trail conditions beforehand.

Can you swim in the lake? It's not recommended, as swimming can disturb the lake's delicate ecosystem.

Is camping allowed at the lake? Bivouacking is tolerated, but only between 7 p.m. and 9 a.m., in line with Pyrenees National Park rules.