Thanks @Willis for the links. I've started watching them. I remember randomly finding an example of a video like this from the Philippines, though I was disappointed that there weren't many fish in it. Certainly plenty in the rivers in Brazil.
Having searched around it is a bit of a D'oh moment that I didn't immediately recognise the fish with yellow splodges and dots as wild type guppies, which explains the live-bearer females in my videos.
I am inspired to try more of this. There's a small river near me in Leicester where off the top of my head I've seen at least nine species of fish, and there are probably more. I think it would justify a biotype video by itself. Though, if I posted 'here' it would be in the Coldwater sub-forum, not Tropical. Willis, I note that you and others are moderators and I assume can advise on suitability of the topic - please do.
I note the equipment they guy in Brazil has. I have all of the swimming equipment that he does except for a snorkel - it was inconvenient having to surface to breathe all the time. Snorkels are cheap and I swim at a big local diving centre with a shop. He has a much better/bigger camera than me, but I think my GoPro did a reasonable job.
I noted that in the port in Kupang (Island of Timor) there were plentiful fish and some coral underneath the pier. But, no time to go swimming and filming there. (And later on I was told that sometimes there are crocodiles there.) Flying over Indonesia, I noted plentiful presumably coral reefs and lakes/rivers/rice paddies.