One of the best things about the state of New York is its parks. They keep their parks in excellent condition, including the 141-acre state park on the north part of Seneca Lake.
Seneca Lake State Park
Seneca Lake State Park is lovely. You can see from the pictures that they have a huge playground with bathrooms right next to it. There is also a substantial-sized splash pad next to the playground. We only paid $7 to get in, which was $1 per person. On the weekends you can use the beach and swim in the lake. They only have lifeguards on the weekends.
There is no camping permitted in Seneca Lake State Park.