An algae outbreak in the James River posed no threat to people, officials said yesterday.

Tests indicate the outbreak, reported last week in Hopewell, was caused by a nontoxic form of blue-green algae, said Bill Hayden, spokesman for the state Department of Environmental Quality.

The river should be OK for swimming and skiing unless scum or discolored water is seen, Hayden said.

Blue-green algae live naturally in the James. Their concentrations can jump up, however, when they are exposed to warm weather, bright sun and nutrients from sewage plants' discharges.

An overabundance of such nutrients is considered the biggest problem hurting the Chesapeake Bay and its tidal tributaries.

When the algae die, they consume oxygen that fish, crabs and other animals need. The algae also block sunlight from the river grasses that fish and crabs inhabit.

The term blue-green algae is a misnomer, Virginia Commonwealth University biologist Paul Bukaveckas said.

The organisms technically are bacteria, although, like green plants, they obtain energy from photosynthesis. They are microscopic, but in large numbers they can form visible clumps.

Contact Rex Springston at (804) 649-6453 or rspringston@timesdispatch.com