NORFOLK – Algae blooms are choking parts of two rivers.

Video: Algae blooms cover 2 Norfolk rivers

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Swirls of dark reddish-brown algae in two sections of the Elizabeth River and along the Lafayette River were spotted Friday by members of the Chesapeake Bay Foundation.

They were still visible Monday afternoon when Sky13 flew over.

Foundation officials were on the rivers taking samples.

According to the Foundation, blooms occur when there’s too much nitrogen and phosphorus.

The growth can block sunlight from reaching underwater plants and so lower oxygen available for marine life.

Algae blooms may be green, brown, or reddish in color, and usually appear cloudy in the water