Kanali Beach is the convenient choice on Poros: close to town, simple to reach, and good for a swim when you do not want to organise transport to the island's quieter coves. It is more practical than spectacular, with the usual summer mix of umbrellas, tavernas, and quick dips.
The beach works best as part of a relaxed day around Poros Town rather than as a destination in itself. Come in the morning or late afternoon if you want calmer water and fewer people, especially in July and August.