Harmful algal blooms [local] can develop when the environmental conditions are right. Most of these are not harmful. Nevertheless neurotoxins are produced that may accumlulate in the food web [local] and be harmful to birds, fish and humans [local]. These red tides can be detected by satellite imagery techniques. Not all algae are harmful. This site [local] explains more about the effects of red tides, the origin of the tides, effect on other organisms and what is safe to eat. Generally shrimp, crab, scallops, and lobsters are safe to eat during red tide and oysters, clams, mussels, mollusk, and whelks are not safe to eat during a red tide.