I had heard about this walk from friends, but no one could give me precise directions as to how to find the start - it's actually very easy to find once you have parked in the free public car park on Calle Mirto and walked the half a mile or so along the road down to the bottom of the valley. There are two other (smaller) car parks closer to the start of the walk, but they fill up very quickly. You need a good pair of old trainers or waterproof sandals, as there's no way to avoid walking in the water up the gorge, shorts or swim wear, a decent hat, sun block and lots of water! It's a great day out (we had 3 teenagers with us) but do start early or, like us, you'll have to turn back before you reach the source - we walked for about 4 hours at a gentle pace but without stopping and still didn't get to the top. The scenery is beautiful (see the photos I have posted) and the water lovely and clear, with waterfalls and pools along the way if you want a rest. In some parts the river bed is fairly wide and shallow and in others it narrows so only one person can fit through at a time and you are wading in knee deep water - if you went when there had recently been rain I am sure it would be much fuller/deeper. Take a picnic for lunch and, if you get to the source, eat it there - if not, you can eat it at one of the pools along the way. We'll definitely be going back and this time we'll start earlier and make better time to be sure we get to the source!
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.