The most common type of reef is the fringing reef. This reef grows outward from the shore, creating a border between the island’s shoreline and the open ocean. Near the shore, the reef is typically flat and shallow, forming a 'reef flat' that is bathed in sunlight and may even be exposed during low tide. As the reef extends further out, it transitions into a steeper slope or drop-off, where the structure descends into deeper waters. This outer edge is often teeming with marine life, nourished by nutrient-rich currents from the open ocean.

When a fringing reef grows upward from a volcanic island that has gradually sunk below sea level, keeping pace with the rising water, it forms an atoll. Over time, this process forms an atoll—a ring-shaped coral reef encircling a central lagoon where the island's peak once stood. The atoll typically has a circular or oval shape, with the reef forming a barrier protecting the calm lagoon.

The lagoon often appears vibrant blue and shallow, contrasting with the deeper ocean waters outside the reef. Gaps or channels in the reef allow water and marine life to flow between the lagoon and the open ocean, adding to its dynamic ecosystem. This creates a stunning natural formation where the volcano's original presence is only hinted at by the circular reef and the tranquil lagoon it encircles.

Barrier reefs are like fringing reefs in that they also border a shoreline; however, instead of growing directly out from the shore, they are separated from land by an expanse of water. This creates a lagoon of open, often deep water between the reef and the shore.

Coral reefs are important because they bring in billions of dollars to our economy through tourism, protect coastal homes from storms, support promising medical treatments, and provide a home for millions of aquatic species.