Lac Petrus

Lac Petrus is a small mountain lake in the commune of Saint-Étienne-de-Tinée, tucked into the upper reaches of the Haute-Tinée valley within the Mercantour National Park. Sitting at roughly 2300 metres above sea level, it occupies a scree-strewn side valley known as the Malignas, just below the historic Chemin de l'Énergie trail. It isn't the largest or best-known lake in this part of the Alpes-Maritimes, but it forms a key waypoint on the routes linking the Vens and Rabuons valleys.

Where exactly is Lac Petrus?

The lake sits on a high-altitude stretch between the Lacs de Vens and Lac de Rabuons, in terrain dominated by rocky ridgelines and loose stone slopes typical of the higher Mercantour massif. Visitors who have walked this section note that the water level has dropped somewhat in recent years, leaving the lake noticeably smaller than it once was — a pattern also seen at several neighbouring lakes in the same valley.

What is the Chemin de l'Énergie?

Lac Petrus lies directly along the Chemin de l'Énergie, a historic walking route that follows former hydroelectric infrastructure built to channel water from high-altitude lakes down to power stations in the valley below. Part of the path runs through tunnels cut into the rock; the section between Plan de Ténibre and Lac Pétrus was closed for a period after rockfalls, and the local department carried out repair works there in 2021 and 2022. This gives the area around the lake an unusual character, mixing traces of engineering history with a genuinely wild high-mountain setting.

How do you get to Lac Petrus?

Most routes start from Saint-Étienne-de-Tinée, from the large car park by the Maison du Parc, just past the local secondary school. Lac Petrus is often included in a longer, multi-day trekking loop that also takes in Lac Fer, Lac des Babarottes, and the Lacs de Vens, continuing on towards the Aiguilles de Tortisse. Shorter, single-day options typically combine Lac Petrus with nearby lakes such as Lac de Rabuons, Lac Chaffour, or Lac du Cimon, forming a loop with varied elevation gain and loss.

What should you know before setting out?

The trails around Lac Petrus run through Mercantour National Park, where nature-protection rules apply: no camping outside designated areas, dogs must be kept on a lead, and picking plants or collecting mineral samples is restricted. At this altitude, weather can turn quickly even in summer, so it's worth checking the forecast and current trail conditions beforehand — the national park publishes updates on path closures, including sections of the Chemin de l'Énergie.

FAQ

How high up is Lac Petrus? The lake sits at around 2300 metres above sea level, in the high-altitude part of the Haute-Tinée valley.

Is Lac Petrus a large lake? No — it's a relatively small body of water, and its surface area has shrunk somewhat in recent years as the water level has dropped.

Where's the best starting point for the hike to Lac Petrus? The car park at the Maison du Parc in Saint-Étienne-de-Tinée, from where trails lead towards the Chemin de l'Énergie and on to the lake.

Which other lakes can be combined with a visit to Lac Petrus? Lac Petrus lies close to Lac Fer, Lac des Babarottes, the Lacs de Vens, and Lac de Rabuons — popular routes link several of these lakes into a single loop.

Are there any special rules to follow near the lake? Yes, the area lies within Mercantour National Park, so nature-protection regulations apply regarding camping, dogs, and collecting plants or samples.