This scene does not come from a B horror movie. Incidents of this type actually occurred periodically at many Black Sea beach resorts in Romania and Ukraine in the 1970s and 1980s. During that period an estimated 60 million tons of bottom-living (or benthic) life perished from hypoxia--too little oxygen in the water for them to survive--in a swath of sea so oxygen-deprived that it could no longer support nonbacterial life.
Reviving Dead Zones
How can we restore coastal seas ravaged by runaway plant and algae growth caused by human activities?
Imagine a beach crowded with vacationers enjoying the hot summer sun. As children paddle about in the shallows, foraging for shells and other treasures, dead and dying animals begin to wash ashore. First, a few struggling fish, then smelly masses of decaying crabs, clams, mussels and fish. Alerted by the kids' shocked cries, anxious parents rush to the water to pull their children away. Meanwhile, out on the horizon, frustrated commercial fishermen head for port on boats with empty nets and holds.