Access: from Crest, follow the D93 towards Allex. At the roundabout very close to the TGV line, turn left towards Écosite. About one kilometre further on, just before the Ail Dromois building, turn right onto the road. Continue straight on for another kilometre until you reach a junction. Turn left, following the sign for the Sentier du Castor. Pass under the railway line to find a car park.
(S/E) At the car park entrance, follow the tunnel leading to the lake (signposted ‘Sentier du Castor’). At the tunnel exit, turn left onto the path that skirts the lake and the marsh. You’ll come to an information board about the small marsh; walk a few steps further, pass a path on your right and head towards the ‘Le Petit Marais’ signpost.
(1) Turn left towards La Petite Crau and cross a wooden footbridge. After a ‘Castor No. 6’ sign, follow the path on the right which leads to La Petite Crau. Continue to the right towards Les Berges de la Drôme; 200 metres further on, you’ll reach the ‘Pipe Line’ marker. Turn left towards the viewpoint overlooking the Drôme.
(2) Turn right onto the path and then left shortly afterwards to rejoin the original path. The path winds through the woods, more or less following the river. A few tracks branch off to the left to get as close as possible to the water. You’ll reach another footbridge (shown slightly out of place on the map).
(3) Turn left to find the ‘Confluence Drôme Merdarie’ signpost. Turn right towards Lac Communal d’Eurre. You’ll soon reach another junction. Carry on straight ahead, then follow the lake to the tunnel. Go through it and return to the car park (start/finish).
