Editing Ibaraki Prefecture (section)

===Water system===
The main rivers that flow through the prefecture include the [[Tone River|Tone]], [[Naka River (Tochigi Ibaraki)|Naka (Ibaraki)]], and [[Kuji River (Ibaraki)|Kuji]] rivers, all of which flow into the [[Pacific Ocean]]. Before the seventeenth century, the lower reaches of the Tone were different from its current layout, and the Tone ran south and emptied into [[Tokyo Bay]], and tributaries such as the Watarase and Kinu rivers had independent water systems.

The main tributaries of the Tone River basin are the [[Kinugawa River|Kinu River]] and Kokai River, which flow from north to south in the western part of the prefecture. The Shintone and Sakura rivers flow into Lake Nishiura.

The [[Edo River]] flows into Tokyo Bay; its source currently rises as an arm of the Tone River. In the past, the course of the Edo River was different, its source was corrected and diverted to the Tone River in the 17th century by the Tokugawa shogunate to protect the city of [[Edo]] (now Tokyo) from flooding.

The Tone River, in addition to the Edo River, is part of the southern border of Ibaraki Prefecture with Chiba Prefecture, and the [[Watarase River]], Tone River, Gongendō River, and [[Naka River (Saitama Tokyo)|Naka River (Saitama)]] in the southwestern border of Ibaraki with Saitama Prefecture. The Watarase River has become a small boundary of the southern border between Ibaraki and Tochigi prefectures.

From ancient times to the beginning of the Edo period, the lower reaches of the Tone River did not exist and the mouth of the Tone was in Tokyo Bay. On the plain was the [[Katori Sea]], which existed in ancient times,<ref>{{cite web|url=http://w.utakura.com/yokokator9|title=歌垣発祥の地を訪ねる「筑波山・香取の海」(in Japanese) - To visit the birthplace of Utagaki「Mt. Tsukuba ・ Katori Sea」-|access-date=November 12, 2021|website=utakura.com|archive-date=October 28, 2021|archive-url=https://web.archive.org/web/20211028211906/http://w.utakura.com/yokokator9|url-status=live}}</ref> the [[Lake Kasumigaura]] and other lagoons in present-day Chiba prefecture are remnants of that sea. Katori Sea was connected to the Kashima-nada (Pacific Ocean).

Lake Kasumigaura is currently divided into three lakes: Nishiura, Kitaura, Sotonasakaura. In addition, in the prefecture there are freshwater lagoons such as Hinuma, [[Lake Senba|Senba]], and Ushiku.

[[Fukuoka Dam]], is a dam that spans the Kokai River in [[Tsukubamirai, Ibaraki|Tsukubamirai]], it is one of the three largest dams in the Kantō region. Ryūjin Dam in [[Hitachiōta, Ibaraki|Hitachiōta]], is a beautiful dam on the Ryūjin River with a large pedestrian suspension bridge above the dam lake.