Do humans cause red tide?

Scientists say there’s evidence that massive blooms may be partly caused by human activities, such as fertilizers washing off farms and the discharge of fertilizer-laden water from Lake Okeechobee into the Gulf of Mexico

What about in general? Is fertilizer only the reason?

Yes because it also comes from chemicals in farming, factories, sewage treatment plants and other sources that dissolved in water on the land. This water flows into the ocean and can cause algae to grow faster, leading to red tides.