Water that runs off buildings, streets and parking lots becomes polluted with auto fluids, fertilizers, pesticides, pet waste and sediment. Run-off that doesn’t evaporate or seep into the ground flows through gutters and storm drains to the nearest stream on a journey to the sea. Contaminated run-off damages coastal waters and marine life with pollutants, algae blooms and particulate matter. Water turbidity increases, blocking out sunlight that sustains plants and seaweeds.

Algae Blooms

Plant-like algae are found in our marine waters wherever sunlight reaches. Swarms of microscopic dinoflagellates. Giant mats of sargassum weed. Over 5,000 species of algae form the foundation of marine and aquatic food chains. Uncontrolled algae blooms devastate coastal ecosystems. Some, like red tide, produce neurotoxins that kill fish, birds and mammals. Algae blooms deplete oxygen in the water, smother reefs and clog the gills of fish and invertebrates. They cloud the water and block sunlight that plants need to survive.

Algae blooms can be caused by nutrient pollution – contamination by nitrogen and phosphorus from fertilizers and cleaners in runoff. Oyster depleted ecosystems that become polluted by nutrients are particularly vulnerable to being overwhelmed by explosive algae growth.

Illustrated chart of the life cycle of an oyster from fertilization to mature oyster


Oysters are nature’s filters and engineers, purifying water and clustering in dense reefs that protect the shoreline. Like clams, mussels and scallops, oysters are bivalves – a class of molluscs named after their hinged shells. Oysters grow one on top of the other, creating bristling, three-dimensional reefs. A community of filter feeders, the reef relies on currents for food and to propagate.

An oyster draws water in through a siphon and strains plankton, algae and small food particles through gills for digestion. Waste is expelled by a siphon to be deposited, decomposed and recycled in substrate. When oysters spawn, currents mix the eggs and sperm they release into the water. Females produce 10-25 million eggs per spawn. Fertilized eggs become free-swimming larvae that develop into spat – immature oysters attached permanently to other oysters, rocks, shell fragments or the substrate.