Authorities found several environmental violations at the luxury property, where workers were building an artificial lake and beach.
It included "carrying out work subject to environmental control without authorization," capture and diversion of river water without authorization, and "removal of land and suppression of vegetation without authorization."
Authorities cordoned off the site last month and ordered all activity to cease, but Brazilian media reported that Neymar threw a party there and bathed in the lake.
On top of the fine, the case will also be investigated by other environmental control bodies. including the local attorney general's office, the state civil police environmental protection office
Neymar's spokesperson has declined to comment on the matter.