There a 2 Options. Going for carp which in late summer should be the best time - or going for perch which can be found also plenty. But same applies - the size is usually rather small. In any case its a worthwhile activity when going to the mountains or the beach since the lake is situated at the entry to the Alpujarras. Its a little difficult to access the lake so the best thing is to park near the dam and walk around (But dont fall - its quite steep at some spots ;)
The Lake in Guajar Sierra, just to mention, is of a different kind. The fish are bigger and it has quite some big trout in there. Thats for a future story to come.