As pointed out by Joonas, in Latin "a number of other swimming verbs are obtained with prefixes you can add to either one: ad-, e-, de-, in-, prae-, re-, tra-, ab-".
As a case study to show the importance of separating genetic from typological classification of languages, I think that the present question becomes even more interesting if (re)formulated in the following terms: why is it the case that Latin, compared to Romance languages, has many complex/prefixed verbs for swimming (e.g., abnato 'to swim away', eno/enato 'to swim out', praenato 'to swim by', reno 'to swim back', subnato 'to swim under', trano 'to swim over', etc.)? To put it in the following typological (not genetic!) terms, why is it the case that, concerning this aspect of word formation, Latin is quite different from Romance languages and, in contrast, is very similar to Slavic languages (where the path/directionality is also typically expressed by a prefix)? So the answer to the interesting question Why there are several words for swimming in Latin is essentially the same to the question Why there are several words for swimming in Slavic. Is there any native speaker of a Slavic language to confirm this typological point?
For those readers interested in knowing more about the previous important typological change from Latin to Romance languages (for example, if you want to know why Joonas's list of Latin verbs above disappeared or is not productive in Romance), I recommend you the reading of the following book:
Finally, as for the interesting typological parallelism between Latin and Slavic, take a look at https://global.oup.com/academic/product/the-morphosyntax-of-transitions-9780198733287?cc=es&lang=en&# (You'll see that both Latin and Slavic belong to the SAME typological class: so-called "weak satellite-framed languages").