I have plants year round outside in Portland Oregon. I'm not familiar with your area, but there should be. What you can grow depends on what is available and your conditions. The corner pond looks like it might get the occasional ray of natural light, but the other one looks to be dependent on artificial lights. I assume you have a pond/garden store that sells water/riparian plants? If not, what is available at your aquarium store? Whatever you get, it'll need to survive low level lighting. I have some plants that survive my dark cold garage during the winter, but not many. If I understand correctly, Malta is a fairly temperate climate, with reasonable temperatures year round. Any water plants endemic to your island?