There are several beaches along the south coast of Poros. They are often very good. In general you can say that the beaches consists of sand and stone, more or less. On some beaches it is difficult to walk into the water because of the stones in the water. On all beaches you can rent a sunbed and an umbrella. The price is about 5 EURO for two beds and one umbrella. I have visited every beach on Poros and will give you a description of them all. Click on the names and you will get there. They are presented from left to right as they are on the map. The beach on the backside of the island, "Vagonia bay", is presented last.
The beaches in Galatas are all east of the city.
They are called "Bouja", "Plaka" and "Aliki beach".
Use the links under the map.