I'm very happy for your indeed. I would love to have such an outdoor pool available to me right now - to complement the Sky Lakes in New Paltz where I began swimming last week (in 13.3C water).
Since your pool has a swimmable length of 125m you might try versions of two practices I posted on this thread
in the OW conference.
For the first you could do
125 - 250 - 375 - 500
or 250-500-750-1000 - 750 - 500 - 250
Hold pace and SPL as you go up; hold SPL increase pace as you come down.
And the second practice is 6 rounds of [4 x 125]