Straight through Santiago del Teide, over the crest of the hill above Valle Ariba, then you will see the "Lake District" on the left. You can park by the bus stop next to the restaurant on the corner, where the junction is with the Los Llanos road which goes off to the right, then walk along the road for a short distance, then take the track down to the left. Alternatively, park in Erjos and walk down the first road to the left, turn left at the church, then down the path on the left at the corner. Keep straight on where another path goes off to the right in about 100 m. Then just follow the path through the Lake District. There is an information sign with descriptions of all the wild life by the first lake. Lovely wild flowers, lots of frogs and water fowl.
This area is also the starting point for several lovely walks in the area, some of which are signposted and documented (the Visitor Centre in Santiago has maps). The walk through the laurel forest and round Montana Gala (the hill above the "Lake District" with the fire watch tower) is a particular favourite.