In the swim means actively involved in a group, activity, or area of life. If you are in the swim, you know what is going on and take part in it. The phrase often suggests being socially or professionally connected, rather than isolated or out of touch.
The image behind it is clear. A swimmer is in the moving water, carried along with the action. Someone on the bank is outside it. That is why the idiom came to mean being part of events instead of being left out.
Writers often use it in social, political, and work contexts. For example, you might say, She likes to stay in the swim of local politics. You could also say, After his career break, he wanted to get back in the swim.
- Use it for being involved and informed.
- It often suggests belonging to an active circle or current of events.
- It is usually more natural in British English than in everyday American English.
So the idiom is not about swimming literally. It is about being in the flow of activity, connection, and current events.