At the moment there are sixteen lakes visible at the surface in Plitvice , but the number changes due to natural conditions. The unique feature of these lakes though are natural dams, called travertines, which are build by a combination of bacteria, algae and moss. They are very sensitive to outside conditions and grow up to one centimeter per year. The lakes are known for their distinctive colours, from azure to green, grey or sometimes blue depending on the light and also on the organisms living inside. But most famous of course are the countless waterfalls, which bind the different lakes together and hereby create a unique natural landscape.