Kris - I have carried out some research myself on this matter as I am planning a European fishing expedition for 1998.
It would appear that anyone who holds a fishing permit 'Carte de P?che' can fish from any common land or any land owned by others where permission is granted by the owner of the said bankside.
Rivers and ponds in France are divided into 1st and 2nd Category (1er et 2eme Categorie) waters. The principal distinction is that on 1st Category waters you need to have an extra stamp on your permit, mainly in order to fish for trout and the other salmonides. This distinction is rendered irrelevant by the holiday fishing permit (Carte de P?che de Vacances), which covers all types of fish and both categories of water. Rivers are patrolled by gendarmes and by guardians de p?che to ensure that anglers have one.
The Carte de P?che de Vacances covers you for 15 consecutive days and currently costs about 28 euros and can be used between 1st June and 30th November. After 30th November and before 1st June an annual fishing permit is obligatory. This currently costs about 60 euros though prices vary from department to department. It may be used for the whole year but only in one department. You can add another 45 departments, effectively covering all the areas we cover in continental France by purchasing a stamp currently costing about 16 euros. This is the stamp of the Club Halieutique. The fishing seasons change slightly every year and vary from department to department. For all fresh water fishing you will need a fishing permit. Fishing is allowed during the season from half an hour before dawn to half an hour after sunset.
I do not know much about the Ari?ge river apart from it rising near Andora and flowing 170 km to become a tributary of the Garonne. The following link may help you a little.
http://www.ariege.com/what_to_do/outdoors/fishing.html
