Question

How does human activity contribute to red tides? In my own words

Answer 1

Short version you can use:
"Red tides are blooms of algae that get out of control. Human activities — like runoff from farms and lawns (fertilizers), sewage leaks, and waste from animal farms — add extra nutrients to the water that feed the algae. Coastal development, dredging, and aquaculture can create calmer, nutrient-rich conditions, and climate change (warmer, more layered water) makes blooms more likely. People also spread bloom-forming species on ship ballast water. In short, we don’t create algae from nothing, but our pollution and changes to the environment make red tides more frequent and worse."

Slightly longer version:
"Red tides happen when certain algae multiply extremely fast. Natural factors matter, but human actions often fuel these events: fertilizers, lawn and agricultural runoff, leaking septic tanks and poorly treated sewage, and manure from livestock dump lots of nitrogen and phosphorus into rivers and coastal waters, which act like fertilizer for algae. Coastal construction, dredging, and aquaculture increase nutrient availability and reduce water movement, while climate change warms surface waters and strengthens stratification—both favor algal growth. Shipping can also move harmful species between regions. Altogether, these activities boost the size, frequency, and toxicity of red tides."