Presque Isle State Park officials have issued swimming advisories for Beach 1, Beach 6, Mill Road Beaches and Beach 9 on Monday due to research sample plate counts.
Beaches under precautionary swimming advisories remain open to the public, but beach users are asked to use caution while swimming.
The advisories will remain in effect until there is no longer a environmental and public health concern.
The advisories only affect the listed beaches. The park has 13 regulated swimming beaches.