A second feature of the pond is that there is always an island, and a bridge to the island. The bridge seems to always be stone, although I am not sure if that is a requirement. The bridge may be a simple bridge, or it may be a Japanese hemispherical bridge. I suspect that the island symbolizes Nirvana, or in Pure-Land Buddhism, the Pure Land, and that the bridge is enlightenment. There is always only one bridge, and the bridge is always inaccessible.