Glacial water, salt water, silt water, freshwater and mountain water flow throughout our planet to form our hydrosphere. When two tributaries or bodies of water flow alongside each other, they can form a beautiful border. This is known as confluence. Con means against or in opposition of something. Fluence is from the Latin fluentia, meaning to flow. What causes the colour difference? It’s all about the density. Think of density as the thickness of the water. Salty ocean or sea water, silt, sand and mud of rivers and the temperatures of glacial water are factors that affect the density of water. When bodies of water with varying densities meet, the dense (thick) water behaves like a wall that makes it difficult for less dense (thin) water to flow into it. Confluence can last a long distance before the waters mix into each other. Eventually they do. It seems impossible that water could form a border within water but there are a few places in the world where it does! We’ve featured four of them. We highly recommend that you research the rest!