Concentrated waste plumes from ocean fish farms don't always dilute quickly and could travel significant distances to reach coastlines, U.S. researchers say. Researchers at Stanford University studied how variables such as tides, current, the Earth's rotation and the physical structure of fish farm pens influence the flow of waste and subsequent possible impacts on waterways and surrounding shoreline. "This study suggests that we should not simply assume 'dilution is the solution' for aquaculture pollution," said Jeffrey Koseff of the Woods Institute for the Environment at Stanford. "We discovered that the natural environment around fish pens can dramatically affect how far waste plumes travel from the source." Dissolved substances from feces, undigested food and other forms of discharge amass near fish pens and can create "plumes" of highly concentrated waste that hold together for great distances from the source, a Stanford release said Thursday. "As the aquaculture industry grows, so will the number of pens that create pollution," researcher Roz Naylor said."The models that we developed for this study can help regulators determine how waste from proposed fish farms might impact the waterways and coastlines both near and far from the pens."