Sea Currents (海流 Kairyū?) are forces of major importance in the World. A Sea Current is a directed movement that determines the way water acts on a sea or ocean. Since the world is predominantly covered with water, currents are used to propel ships to certain destinations at greater speed. Currents are usually created by changes of temperature in the water, differences in salinity levels (the concentration of salt), tides, wind and the continuous break and mixing of waves, though there are some exceptions. In the World of One Piece, it is even possible to use currents created by massive sea life. The only place where one cannot find sea currents are in the Calm Belts. The Grand Line  itself is thought to be one enormous constantly changing current that separates the seas.
Type of CurrentsEdit
Surface currents are currents found in the warmer waters closer to the surface, and are quite fast moving.
Deep currents are currents found in the cooler waters closer to the sea bed, and are quite slow moving. It is said that if a ship enters the wrong deep current, it can be trapped in the current for over two thousand years before it can reach the sunlight.
Whirlpools are natural forces of disasters that form a sinkhole in the water which can draw nearly anything into its depths. In One Piece, there are two ways for a whirlpool to form.
The first is when a strong current encounters an obstacle, forcing the current to turn in on itself. Such examples are shown with Commander Pudding Pudding, who went up against the Arlong Pirates, the Long Whirlpool at Long Ring Long Land, and with the whirlpool formed by the Tarai Current in front of the Gates of Justice at Enies Lobby.
The second is caused in cases of extreme differences between hot and cool water, which causes the water to rotate in order to find a constant temperature. Such examples are shown with the Knock Up Stream and with the eruption that took place when the Straw Hat Pirates were descending to Fish-Man Island.
- Further information: Reverse Mountain
Reverse Mountain (リヴァース・マウンテン Rivāsu Maunten?) is a place where the currents of the four Blue Seas converge and flow giving an entrance to the Grand Line. The currents are extremely powerful as they are able to pull ships up a steep slope. This is due to the fact that the mountain, being a "Winter Island" using Grand Line terminology, is much colder than the surrounding sea in the four Blue Seas, but not colder than the Grand Line. However, the mighty currents also cause many ships to crash onto the mountain side due to difficulty in steering into the mountain's opening.
Knock Up StreamEdit
- Further information: Knock Up Stream
The Knock Up Stream (
- Further information: Milky Road
The Milky Road (
On Long Ring Long Land, around one of the ten islands that make up the whole, is a large whirlpool. The Long Whirlpool (ロングワールプール Ronguwārupūru?) forms between a 'forest' of Long Corals and the Long Gap, and as its name suggests, it is a long oval shaped whirlpool. This phenomena creates a series of currents amongst the Long Coral forest. If one enters the forest through the wrong current, they will find themselves being turned back, though the correct one will accelerate them towards the whirlpool.
- Further information: Tarai Current
The Tarai Current (タライ海流 Tarai Kairyū?, literally translated as "Tub Current" or "Basin Current"; called Tub Current in the VIZ and FUNimation subs), is a massive whirlpool that connects the three major World Government facilities. Its flow is controlled by the three Gates of Justice, and will either flow or cease based on how much of any of the three gates are opened. The current goes in a circle within the three gates, and is faster for ships to travel using this current than going around the perimeters of the gates to reach any of the three Government facilities. However, this only works if the Government is willing to open the gates for the said passengers. Marines can travel peacefully through this current coating the hulls of their ships with Seastone.
The Serpent Currents (遊蛇海流 Yūda Kairyū?), also known as the Sea Snake Currents in the FUNimation dub, are found on the way to Fish-Man Island, somewhere between the Florian Triangle and the Red Line. These are a series of currents that tend to leap out of the water. They differ between the anime and manga.
In the manga, they form arches and the Straw Hats are briefly seen riding one.
In the anime, they act more like geysers, shooting straight up, but then bending and coming back down. The Straw Hats had to battle through them before they could proceed any further.
The Downward Plume (下向きプルーム Shitamuki purūmu?) is described as a massive underwater waterfall. The only one seen in the series is located near a Winter Island that forms part of the Red Line. It goes under the Red Line and is used to get to Fish-Man Island more quickly. It functions slightly similarly to Reverse Mountain although in the opposite direction, the cold water coming into contact with the Red Line is blasted down towards the ocean floor, moving hot water upwards. A "plume" is the hydrodynamics term for a column of fluid (gas, liquid, plasma, etc.) moving through another and, usually, following its flow. Attaining to the explanation on the series and the scientific term, this is where the "plume" of the name is taken from.
The Grand FallEdit
The Grand Fall (グランドフォール Gurandofōru?) is a non-canonical current that occurs in Dead End Adventure. It appears on Hannabal Island, an island with several rivers that lead to the peak of a mountain. There, a phenomenon occurs once every few years, where both the sea and wind currents reverses, heading uphill to the peak of the mountain. The name Grand Fall comes from the sheer waterfall at the peak, which the currents lead to. This current is used by pirates in an event known as the Dead End Race as the starting line.
Concludes non-canon section.
White Strom (
A common phenomenon in the New World, a Sea Slope (海坂 Unasaka?) is a current that goes "downhill" in the open sea. Ships make great time if they slide down, though presumably go much slower if they were to climb up.
The Rabbit Wave (うさぎ なみ Usagi Nami?) is a wave with rabbit faces appearing on its curl. It only appears briefly in the manga and was unnamed, with the Thousand Sunny sailing on it on the Straw Hat Pirates way to Dressrosa from Punk Hazard. It was named in the non-canon Caesar Retrieval Arc, where it is shown to be a current created by a large number of Sea Laphans, used in order to inhibit the Thousand Sunny. After they were freed from their master, the Sea Laphans used it again to reunite the Straw Hats.
Thrust Up StreamEdit
The Thrust Up Stream (突き上げストリーム Tsukiage sutorīmu?) is a non-canonical current that occurs in the Z's Ambition Arc. It appears in the Maubeugemour Sea near the Red Line, and can be best described as a scaled-down version of the Knock Up Stream. Its power is enough to lift up and destroy a a warship, and though it appears briefly, it has a high frequency of appearances in a given area. Once it starts, even skilled navigators will have no way of knowing where it will pop up next. Unlike with the Knock Up Stream, no whirlpools are created during its formation.
Mixed Juice CurrentEdit
A current found in the waters of Totto Land in Episode 789. The Mixed Juice Current (混合ジュースの流れ Kongō jūsu no nagare?) appears at the intersection of three juice seas, a watermelon juice sea, a peach juice sea and an orange juice sea. Dangerous creatures, such as the Fruit Footballfish, are caught up in these currents, making them quite dangerous.
Concludes non-canon section.
Climbing Koi WaterfallEdit
The Climbing Koi Waterfall (恋の滝を登る Koi no taki o noboru?) is a special waterfall that flows from Wano Country into the New World. It's one of two only known ways to access the country by ship, which is achieved through the help of gigantic koi that swim upstream periodically. It's possible to sail up the waterfall by tying the swimming koi to one's ship through ropes, letting them pull it along as they climb. Doing so successfully allows access to Wano Country's surrounding seas. However, the currents around this waterfall are rather strange, as at its base is a river with a powerful current that goes towards the waterfall, while at the top is a massive whirlpool. That which is pulled in by this whirlpool usually end up getting washed up on Kuri Beach. 
- Despite not being a sea current, the Sandora River is noted to be losing strength and letting the ocean slowly overtake it with seawater, to the point marine animals like the Kung-Fu Dugongs can comfortably live upstream.