It's about how you're swimming as well.
Lots of people think they're doing exercise and losing weight because they're swimming. Which, technically, they are - they're going forwards. But, actually, if you swim 'properly' (for lack of a better phrase) and propel yourself through under the water it is far more effective (not only for fat loss but also for speed).
I used to swim competitively, and still coach. The big mistake people always make is thinking they are really putting in effort when, actually, they were barely moving/pulling with their arms and instead relying a lot on their legs and momentum from the overhead phase of their stroke on freestyle.
Most of the 'force' of many people's forward propel with their arms in freestyle actually comes from the overhead phase and the momentum gained there rather than the push through the water phase (if that makes sense). It'll feel like you're putting in effort under water, because there's water resistance and you've got the momentum from the overheard bit, but trust me...you'll feel real strain when you really start pulling through the water.
Next time you go for a swim and do freestyle, really push your hand through under the water toward you and then pull it* *backwards. Don't be passive about it and don't allow the momentum from the overheard phase to guide you. You could even do it out of the pool today to test the difference. Do your usual crawl and then try it pushing down and pulling backwards. You'll feel the difference. I know I do when I show my classes the mistakes their making.
I'd also be careful with kickbuoys, too many people don't use them properly and it can cause serious joint issues if used for extended periods in the wrong position as well as pretty painful backache!
That might sound lecturing, and sorry if it does, but I see the push/pull mistake all the time at the pool (and hear people complaining about it in the changing room) and always bite my tongue as I don't want to offend or pipe up!
Swimming is great for toning and muscle strength, but it does require a lot more effort to really see results than a lot of people think. It's one of those things where people will churn out length after length after length with poor stroke technique, but actually 1/4 of the length with better technique will tone you more 😊