SAN DIEGO (FOX 5/KUSI) -- The Tijuana River sewage crisis has been happening for decades and has been at the center of ongoing environmental and public health policy discussions between politicians at the city, state, county and federal levels.

For several years, residents in South Bay communities have had to live with the stench and other inconveniences stemming from the raw sewage flowing from south of the U.S.-Mexico border and into San Diego County. • The Nexstar Media Wire video above explains what the different air quality categories mean.

County officials say the odor is due to an elevated presence of hydrogen sulfide (H2S), which is described as a colorless gas with a "rotten egg" smell.

The San Diego County Air Pollution Control District (SDAPCD) measures the amount of H2S in

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