what is on the bottom of my pool

[localh67]

I live in Connecticut and have an above ground pool. My dad has had the pool for about 15 years and this year suddenly we keep finding these small things floating at the bottom that almost look like tiny tried up mulberrys but they but are black in color but just turn to mush when you try touching them. We arent sure what they are and my dad is hoping its not some animal droppings that may be swimming in our pool at night. Im posting some pictures. If anyone has any idea what they could be please let me know. THANKS!

Here are some pictures of what we keep finding floating at the bottom of the pool...