But what causes red tides? Algae. Lots of microscopic plants (thousands/millions of cells per milliliter) that bloom at the same time. Scientists refer to them as "harmful algal blooms" or HABS. Red tides can last a few days to months depending on nutrients, sunlight, water temp., wind, etc. Some algal species produce powerful toxins that can kill fish, shellfish, mammals, and are unhealthy to humans. The National Oceanographic and Atmospheric Association (NOAA) and other organizations track these algal blooms.
So, if hot southern destinations are on your schedule in December/January (lucky you!), see if they are susceptible to red tides. You might want to enjoy the swimming pools instead.