Lakes between Valencia and Madrid???

Does anyone know of the lakes near the road between Valencia and Madrid? I passed them on my way to Madrid and they were an amazing colour. Very aqua coloured. Some sort of mineral deposit must colour the water that way. Does anyone know anything about them?
Is it safe to go into the water ?
Where they are exactly?
Anyone who has travelled between Madrid and Valencia must know of them.

I think it's embalse de Contreras, it's an artificial water reserve made in Cabriel river. There is another one some km before in river Júcar, the embalse de Alarcón.
It's completly safe as the colour is natural because of the plants of the water or minerals of the land close to the river, although i don't know if it will be allowed to swim inside. Maybe you can find more information looking for Contreras or Cabriel.