The ocean is blue because water absorbs most parts of the red spectrum of light. The part of light that is reflected back to us is mostly from the blue spectrum of light. This is why the ocean appears to us as being blue. Many lakes and rivers around the world come in other colours, usually because of algae or minerals in the water, or both. For example, Lake Hillier in Australia is pink in colour. Scientists are not sure why the water in this lake is pink, but they think it is because of algae. The Blue Lagoon in Iceland is a geothermal pool that is blue in colour due to minerals, silica and algae in the water. Laguna Colorada in Bolivia is scarlet in colour, due to red sediments and algae. The Yellow River in China is yellow due to the large amount of silt in the water. Most of these lakes and rivers are still safe to swim in, and the minerals and algae do not pose a danger to human beings unless consumed in large amounts. However, some of these water features may contain high amounts of minerals like sulphur which has a strong smell that is unbearable to some, like the Devil’s Bath in New Zealand.


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