Hull Bright does exactly what its name suggests. It makes your boat's hull...bright!

Made specifically for the brown waterline stains that boats get when in lakes and rivers and also the algae that fishing boats get in the ocean when moored for extended periods. 

From the DJV team:

We love our bright, white boat but as we get it into the Murray at Echuca that stain will start coming up. Hull Bright is an essential part of cleaning our boat every weekend and just like magic, it brings back that new boat shine! Works perfectly, every single time!