Istan Lake, or La Concepcion Reservoir, is the huge lake created by the dam built above Marbella. 
This stunning lake, over 8km long, and easily visible from the road up to Istan, only a few km north of Marbella and Puerto Banus, is a great place for leisure activities.
Tranquil and hardly used, the lake provides fresh water to those living in the Marbella area.
I had the pleasure of going kayaking on Istan lake yesterday evening. For such a stunning location it's amazing quiet - we saw only one other couple out on the water fishing - so plenty room for our three kayaks!
In additon to kayaking, Lars Walker and his team at Ticket-To-Ride based in Puerto Banus, offer a range of exciting activities on Istan Lake, including the very strange looking Aqua Skipping and eco friendly electric Istan Lake Gondola Tours.
Highly recommended, especially in the summer heat!