
The Cabrec mill stream flows along the bottom of the valley. Fed by streams rising near Guern and Poulgroix, it created the water reserve for the forest upstream. Here, lined with characteristic wetland vegetation of sedges and rushes, it once fed the Cabrec grain mill 800 metres below. A sub-tributary of the Blavet, it mixes with the Moulin de Tallené stream at Grand Plessis, then with the river at Sebrevet, between Lanvaudan and Quistinic.