Consuelo
The colour of water bodies may be a product of dissolved salts and/or algal activity, but is more usually a function of (Bean - help me out here) the water's depth, turbidity, surrface conditions, the colour of the bed and the amount of water in the atmosphere above it (which has an impact on the colour of the sky). Frinstance, shallow tropical seas are a beautiful aqua because of all the white (often pure silica or calcium)sediments.
Famous examples of which I am aware are the unbelievably blue blue of the crater lake at Mount Gambier, South Australia and the candy pink of Pink Lake
(and why's it called Pink Lake? - we are but simple folk!! near Esperance, Western Australia. Last time I heard, the Mt Gambier blue (good pic at
http://www.mountgambiertourism.com.au/ was thought to be a function of elevated calcium content at certain times of the year. This may be the same explanation for your lake. The pink lake phenomenon (not restricted to the lake near Esperance I might add - they are quite common) is (I believe) due to a "bloom" of pink algae.
Other chemicals that could give a blue colouring to water would be copper or cobalt. In my experience however, copper rich waters are green. Either way, I wouldn't want to be swimming in the thing.
stales
