Neptune's shaving cream perhaps....

... or natural detergent - like chemicals which
cause phytoplankton blooms. The waves,
especially in big seas, can whisk these
chemicals into a foamy mass. They are
usually an indication of a healthy sea as
the breakdown of the bacteria in such
blooms is beneficial and unlikely to
cause any damage to aquatic life due to
oxygen deprivation as could be expected
were such blooms to be present in a lake
or river.