Image from 2004 Manhattan Island Marathon Swim
From the Roosevelt Island Operating Corp. Ask Erica feature for 1/9/08:

Hi Erica,
Can you please tell me if the open swim times on Tuesdays, Thursdays, and Saturdays, are still open? The website says so but I had heard that the pool might be stopping the open swims.

Thanks.
Jason

Hi Jason,

Due to the community’s request, we have modified the open swim schedule for the winter season. The new schedule is as follows:

Open Swim
Adults Only
When: Tuesday 6:00 – 9:00 & Saturday 4:00 – 7:00

All Ages
When: Thursday 6:00 – 9:00 & Saturday 12:00 – 3:00

Anyone under 18 Must be accompanied by an Adult

Where: Sportspark Swim Center – East side entrance 250 Main Street

Seniors Swim Free at ALL Open Swim Times

For additional information please call Carol Rubino at 212-832-4569.

More on Roosevelt Island swimming here and here.