Ostrov Borok (Russian: остров Борок) is a natural monument listed among the protected areas of Ulyanovsk Oblast in Russia.

The territory is heavily forested, and its trees are home to a large colony of grey herons, with approximately 403 breeding pairs.

The nitrogen-rich soil allows nettles and celandine in to grow large quantities.

Birds are common here, including black hawk, cheglok, sea-eagle, vyakhir, coast swallow, the eastern Zavirushka bluebird, finches, seagulls, and krachki.

Felling trees is forbidden in this territory and human visits are limited to fishermen, hunters, and scientists observing the biocenosis.