Belgian Pool, Hot spring in Upper Geyser Basin, Yellowstone National Park, US.

Belgian Pool is a circular hot spring in the Upper Geyser Basin with pale blue water filling its center. Westward from the main vent, orange and brown algae formations spread across the shallower areas.

Originally named Oyster Spring, the feature was renamed Belgian Pool after a visitor from Belgium fell into it in 1929 and died. The water, about 82 °C (180 °F), is cooler than other springs nearby but hot enough to cause severe thermal burns. References to a "Belgian Geyser" in the 1930s may refer to this same spring.

The name Belgian Pool replaced Oyster Spring after a visitor from Belgium fell into the water in 1929 and died; the older name still appears in some references. In the 1930s the feature was sometimes called the Belgian Geyser, a sign of how loosely thermal terms were used then.

The spring sits at high elevation and the water reaches about 82°C (180°F). Visitors should keep a safe distance from the edge and stay on marked pathways around the feature.

The pool remains cooler than neighboring hot springs, allowing specific algae species to thrive in its shallow western section. This temperature difference creates a distinct biological community not found elsewhere nearby.