Neat photo. It looks like a 'convergence line' were two water masses
meet, often with one of them having an up-welling component. Surface
debris collects along these lines and if there is upwelling, submerged
material like plankton may be brought to the surface along these line.
Both fish and birds may be found feeding along convergence lines. A
gill net fisherman try to avoid convergence lines because they will
'catch' all of the accumulated debris in their net and the net will be
swept-ed out of line. Clutter nets fish less effectively and have to be
cleaned.

Richard Fleming
Green Lake, Seattle