The number of islands for more than three centuries of St. Petersburg's history has been constantly changing. Actually, the history of the city began in 1703, when the first stone of the Peter and Paul Fortress was laid on Zayachiy ("Hare") Island (ZAJ). At that time, in the Neva delta there were 25 natural islands formed by the branches of the Neva river. Now no one dares to give an exact answer to the question "How many islands are there in St. Petersburg?". You can find numbers from 33 to three hundreds in different sources.
There is no clarity about how many islands are actually located in St.Petersburg. In addition, in the Gulf of Finland there is the so-called Kronstadt archipelago, which includes the island of Kotlin, on which the city of Kronstadt is located, as well as 21 forts of the same name fortress (of which 17 forts lie in the administrative borders of St.Petersburg). The total area of the islands is about 80 km² (6% of the total area of St. Petersburg within the administrative boundaries or 14% of the area of the inner city line).
By the time Petersburg appeared, there were fewer islands than we can find now.
In the XVIII century, with the installation of numerous ducts and canals, the number of islands increased. However, many of the canals were soon filled up: in 1737, previously dug canals on the site of the current lines of Vasilyevsky Island disappeared. By the beginning of the 19th century, as a result of the installation of numerous artificial channels, there were 101 of them. Since the middle of the 19th century, work began on landscaping the city center, accompanied by backfilling of some water bodies and waterways, which led to a decrease in the number of islands.