How the Panama Canal Works
Walk Through It in 10 Steps

In January 2025 I stood on the Miraflores viewing deck and watched an enormous car carrier climb step by step in the chamber right below us (→ Panama series ③: Visiting the Miraflores Locks). The motion of the ship rising on water is obvious once you see it. The whole canal, though — Caribbean to Pacific, three lock systems, two lakes — never quite assembled itself in my head from a single vantage point.

So I put together a small interactive panel that walks through the whole transit in 10 steps. The ship is lifted at Gatun, crosses Gatun Lake, threads the Culebra Cut, then drops at Pedro Miguel and Miraflores back to the Pacific. It runs in your browser; you can step through it or play it back.

A 26-metre staircase of water

The Panama Canal is a lock-type canal: it lifts ships across an artificial lake that sits above both oceans by raising and lowering the water level in chambers. On the Caribbean side, the three-chamber Gatun Locks lift a ship up to Gatun Lake (about 26 m / 85 ft above sea level). After crossing the lake and the narrow Culebra Cut (Gaillard Cut), the descent on the Pacific side is split between Pedro Miguel (one chamber) and Miraflores (two chambers). The original chambers are 33.53 m wide and about 305 m long — early-20th-century civil engineering at a scale that's almost easier to admire once you've watched a 200-metre carrier squeeze through.

All filling and draining is done by gravity; no pumps. The Panama Canal Authority (ACP) is explicit about this. The whole system is designed so that water from the lake above falls into the chambers below — which means the real motive power of the canal is, in the end, rainfall.

A rain-fed canal, and a chronic water problem

The canal runs on Gatun Lake, which is replenished only by rain. A single lockage releases roughly 200,000 tons (about 200 million litres) of fresh water out to the ocean. Across normal operations, the canal consumes on the order of seven billion litres of fresh water a day. That makes it acutely sensitive to the dry/wet-season balance — and to longer-term shifts in rainfall.

2023 was one of the driest years on record in Panama. A strong El Niño and continued global warming squeezed the rainy season, and by January 2024 the level of Gatun Lake was about two metres lower than the same month a year earlier. The ACP cut the daily transit cap from the usual 38 ships down to as few as 22. Total cargo through the canal in FY2024 (Oct 2023 – Sep 2024) came in about 29% below the previous year (511.1 M → 423 M tons, PC/UMS).

One technical answer to this lives in the 2016 expansion. The new Agua Clara Locks (Caribbean side) and Cocoli Locks (Pacific side) each have three chambers, plus nine water-saving basins per flight (three per chamber). Instead of dumping each chamber straight to the sea, water is staged into the side basins and reused on the next transit. The Authority's figures are that this scheme reuses about 60% of the water and uses roughly 7% less water per transit than the original locks. Demand keeps climbing, though, and the same lake water also feeds the drinking-water supply of Panama City — meaning every passing ship is, indirectly, competing with municipal taps.

What the canal means for Japan

Operationally that's the picture; for Japan it's also a story about supply chains. In the ACP's FY2024 statistics, the top three countries by tonnage of cargo origin/destination were the United States (~160 M tons), China (~45 M tons) and Japan (~30.7 M tons). Japan accounted for about 14.6% of total canal traffic, placing it third overall.

Historically, Japan was the canal's second-largest user for many decades after the United States, only being overtaken by China in the late 2010s as US–China trade exploded. The route remains essential for Japan's east-coast US trade — grain, LNG, automobiles — and the major Japanese ocean carriers (NYK, MOL, K-Line) count Panama among their most important chokepoints. So when the 2023 drought forced cuts to daily transit numbers, the effects rippled across the Pacific into Japanese supply chains as well.

Back to the deck

Once the mechanism is in your head, the on-site view changes. Looking straight down from the Miraflores deck, you could see there was almost no gap between the hull and the chamber wall — and that the geometry comes essentially unchanged from the original 1914 design. That's the sort of thing that lands faster after you've walked the diagram once. The longer record of just watching a transit happen is in Panama series ③: Visiting the Miraflores Locks.