Discoloured water
Patches of unusually coloured sea — often a sign of a submarine volcano or of a shoal.
Yellow, green or brown water over deep sea can mean volcanic gases and minerals rising from an erupting submarine volcano. Japan's coast guard regularly reports discoloured water around active volcanoes south of Honshu, and the warnings that follow keep ships clear of the vent. Discoloured water over a shallow area can also mean the depth is less than charted.
A report of discoloured water records what was seen. It does not establish that an eruption is happening.
What the archive shows
99 messages in this archive use “Discoloured water”, the earliest issued 1988-01-26 and the latest 2026-07-17. 8 of them are in force in the latest lists we collected. A hazard reported again and again counts once per message.
The largest yearly count is 2006, with 12 messages. Collection is incomplete between 2024-05 and 2026-08-17, so 2024, 2025 and 2026 are not comparable with fully collected years.
Volcanic accounts for 93 of 99 recorded messages (94%), the largest warning type group in this selection.
Located messages that use it fall in 8 sea areas; the most frequent are Philippine Sea (58), North Pacific Ocean (15) and South Pacific Ocean (13).
Messages that use it are issued most often in January (12 across all years) and least often in December (3).
By warning series: HYDROPAC 83, NAVAREA XI 7, NOAAORR 4 and HYDROLANT 2, and 2 more.
Messages using it, by year of issue
By month of issue, all years
Where it appears · 8 sea areas
In force now · 8
- HYDROPAC 2039/26 · Volcanic · North Pacific Ocean2026-07-16 · in force
NORTH PACIFIC. NORTHERN MARIANA ISLANDS. 1. DISCOLORED WATER WITH INCREASED LIKELIHOOD OF SUBMARINE VOLCANIC ACTIVITY REPORTED IN VICINITY 20-26.00N…
Discolored water with increased likelihood of submarine volcanic activity reported in vicinity 20-26.00N… → - NAVAREA XI 322/26 · Volcanic · North Pacific Ocean2026-07-16 · in force
NORTH PACIFIC, MARIANAS. DISCOLOURED WATER REPORTED IN VICINITY OF 20-26.0N 145-01.0E AT 160013Z JUL. CANCEL 0020/24.
Discoloured water reported in vicinity of 20-26.0N 145-01.0E at 160013Z jul → - NAVAREA XI 491/24 · Volcanic · Philippine Sea2024-09-19 · in force
NORTH PACIFIC, NANPO SHOTO. DISCOLOURED WATER OBSERVED IN VICINITY OF 31-26.4N 140-03.0E AT 180545Z SEP. VESSELS REQUESTED TO BE…
Discoloured water observed in vicinity of 31-26.4N 140-03.0E at 180545Z sep → - NAVAREA XI 206/23 · Volcanic · Philippine Sea2023-06-14 · in force
NORTH PACIFIC, NANPO SHOTO. DISCOLOURED WATER OBSERVED IN VICINITY OF 25-27.1N 141-14.5E AT 140425Z JUN. VESSELS REQUESTED TO BE…
Discoloured water observed in vicinity of 25-27.1N 141-14.5E at 140425Z jun → - NAVAREA XI 207/23 · Volcanic · Philippine Sea2023-06-14 · in force
NORTH PACIFIC, NANPO SHOTO. DISCOLOURED WATER OBSERVED IN VICINITY OF 24-17.2N 141-28.8E AT 140350Z JUN. SUBMARINE VOLCANIC ERUPTION…
Discoloured water observed in vicinity of 24-17.2N 141-28.8E at 140350Z jun → - NAVAREA XI 326/21 · Volcanic · Philippine Sea2021-10-13 · in force
NORTH PACIFIC, NANPO SHOTO. DISCOLOURED WATER OBSERVED IN EXTENDING SOUTH FOR 5 MILES, 2 MILE WIDE, FROM 27-16.7N 140-56.6E AT 120643Z…
Discoloured water observed in extending south for 5 miles, 2 mile wide, from 27-16.7N 140-56.6E at 120643Z oct →
How it reads in recent messages
- HYDROPAC 3071/24 · Volcanic · Philippine Sea2024-09-19
PHILIPPINE SEA. JAPAN. DNC 12. 1. DISCOLORED WATER REPORTED IN 31-26.40N 140-03.00E AT 180545Z SEP. 2. CANCEL HYDROPAC 2440/24.
Discolored water reported in 31-26.40N 140-03.00E at 180545Z sep → - HYDROPAC 153/24 · Volcanic · North Pacific Ocean2024-01-13
WESTERN NORTH PACIFIC. NORTHERN MARIANA ISLANDS. DNC 12. DISCOLORED WATER WITH INCREASED LIKELIHOOD OF SUBMARINE VOLCANIC ACTIVITY REPORTED IN 20-25.00N…
Discolored water with increased likelihood of submarine volcanic activity reported in 20-25.00N 145-01.00E… → - HYDROPAC 12/24 · Volcanic · North Pacific Ocean2024-01-01
WESTERN NORTH PACIFIC. NORTHERN MARIANA ISLANDS. DNC 12. DISCOLORED WATER WITH SUBMARINE VOLCANIC ACTIVITY REPORTED IN 20-25.2N 145-01.8E AT 012230Z JAN.
Discolored water with submarine volcanic activity reported in 20-25.2N 145-01.8E at 012230Z jan → - HYDROPAC 2986/23 · Volcanic · Philippine Sea2023-09-19
WESTERN NORTH PACIFIC. NORTHERN MARIANA ISLANDS. DNC 12. DISCOLORED WATER WITH SUBMARINE VOLCANIC ACTIVITY REPORTED IN 15-37.00N 145-34.00E AT 190306Z SEP.
Discolored water with submarine volcanic activity reported in 15-37.00N 145-34.00E at 190306Z sep → - HYDROPAC 1982/23 · Volcanic · Philippine Sea2023-06-14
PHILIPPINE SEA. JAPAN. DNC 12. 1. DISCOLORED WATER REPORTED IN VICINITY 25-27.10N 141-14.50E AT 140425Z JUN. 2. CANCEL HYDROPAC 1568/23.
Discolored water reported in vicinity 25-27.10N 141-14.50E at 140425Z jun →
Earliest in the archive
- NOAAORR-6547 · Spills · The Coastal Waters of Southeast Alaska and British Columbia1988-01-26
…carrier tied up at the Skagway, Alaska, dock, noticed a leak. The smell of gas fumes and discoloration of the water were the initial indications that gas was leaking at an unknown rate from a…
At about 0800 on january 26, 1988, the M/V frank h. brown, a canadian cargo and fuel carrier tied up at the… →
Often in the same message
Related terms
- Volcanic activity
- An erupting or restless volcano near or under the sea, with a keep-clear radius around it.
- Pumice
- Light volcanic rock floating in rafts after a submarine eruption; it can clog engine cooling intakes.
- Shoal / reported depth
- Water shallower than the chart shows — a newly found shoal, a reported depth, or less water than charted.
Warning types that use it
- Volcanic — Submarine eruptions, discoloured water, pumice rafts.
Counts cover the messages in this archive that use the term, recounted 2026-09-24; see coverage for what is collected and since when. Not for navigation — follow official NAVAREA and coastal broadcasts.