Question: Why are red tides produced? Are they harmful?

Hi!
Red tides are a type of algal bloom and they actually have nothing to do with tidal activity.
An algal bloom is caused by the rapid accumulation of phytoplankton (which are micro-algae floating in the water) populations. These often happen close to the coast and when the conditions in the water are particularly good for the life of these microorganisms, which can reproduce really fast. So for example when a lot of nutrients (nitrogen, phosphorus, carbon, silica, …) are available in the water and there is plenty of sun light, there can be an algal bloom.
These algal blooms are called “red tides” when they are caused by specific species of phytoplankton containing red photosynthetic pigments which give them a red or brown colour (instead of green, when they mainly contain chlorophyll).
Not all red-coloured algal blooms are harmful. So actually the term “red tide” is often used to describe harmful blooms, but this is not entirely accurate.
Some of these red-coloured plankton species can be harmful as they release toxins which can kill fish and birds that feed on them, larger marine mammals (e.g. dolphins), and other organisms. They can also be dangerous for humans as they can affect people with respiratory diseases and cause poisoning when contaminated shellfish is eaten.