City officials ordered the closure on Wednesday after they say a grease blockage caused about 15,000 gallons of sewage to spill into the Rubio Wash, which leads to the Los Angeles River.
"Water from the Los Angeles River connects to the Pacific Ocean in Long Beach, which means pollution anywhere upriver can affect the coastal waters and other waterways in the city," the city said in a statement.
Officials say the sewage will eventually make its way to the shores of Long Beach, prompting swimming areas west of Belmont Shore to be closed.
Long Beach City Health Officer Dr. Anissa Davis says the areas will remain off limits until the water quality meets state requirements.