Like most of us, you probably assume you know what somebody looks like when they are drowning and/or need help in the water. You may not be right.
Read this article and keep it in mind when you’re near the water. My short version (please read the entire thing for details) is "if they are making noise/can answer questions, they probably are ok… if not, then check on them!".
Not to say that people yelling for help don’t need it… they are often in the earlier stages of distress, but apparently when somebody is really drowning, making noise becomes about impossible. Kind of like asking a choking victim if they are ok… if they can talk or cough, they can breathe.