[Not a teacher]
When we talk about repeated actions in the past, we use simple past (swam), but the past continuous is also possible if we want to express the idea of repeated actions for a limited or temporary period in the past.
When I was on holiday, I swam/was swimming in the sea every day.
Moreover, the past continuous is used when the repeated action is also the background to something happening at the same period.
Student or Learner