You nailed it. The more nutrients in the water, the more stuff grows. Here in western LIS we have one of the highest growth areas anywhere. It's surrounded by urban and suburban runoff including lots of manicured (well fertilized) suburban lawns and golf courses, and tidal wetlands. The water is turbid and it's rare to be able to see more than about 4-5 feet underwater.

Unpainted lines and dinghy bottoms grow starter slime and little seed barnacles within a week, and after 2 weeks warrant power washing or wiping. After 4 weeks "fuggetaboutit". They catch pickled herring here also.