Tracking marine dumping

Introduction

Dredging and dumping of marine sediment is a regulated but poorly monitored practice. In Denmark, as in many other countries, harbors regularly dispose of sediment at sea, often under permits issued by environmental agencies. But how can we know if dumping actually happens where it is allowed?

This guide shows how you can track dumping operations using publicly available AIS ship tracking data, KML zone files from environmental authorities, and – in the Danish case – declarations obtained via Freedom of Information requests.

The methods presented here are based on a project supported by the Velux Foundation and carried out by the NOIR team. They can be used by journalists, NGOs, researchers or engaged citizens.

What is dumping?

Dumping of dredged material goes by many names. In Denmark, it’s commonly referred to as “klapning”, but it may also be described as “disposal of sediment,” “deposit of sediment,” or “dumping of sludge.” In EU legislation, the practice is officially termed “relocation of sediment.” In short, dumping is the process of disposing of dredged material at sea, typically carried out by ports and harbor authorities. The primary motivations include:

Maintenance of navigation channels (to keep waterways deep enough for vessels)
Harbor expansion and construction
Port infrastructure upgrades

When harbors are dredged, sediment that may have been undisturbed for decades is stirred up. This sediment often contains harmful substances — for example, TBT (tributyltin), a toxic chemical previously used in ship hull coatings. Dumping such material into the sea can reintroduce pollutants into marine ecosystems, harming biodiversity and water quality.

Authorities often allow dumping if contamination stays within legally defined limits for substances like heavy metals and organic toxins. These limits are based on laboratory testing of sediment samples before the operation begins conducted by the harbours and ports.

In Denmark, as in many other countries, this permission is typically restricted to specific geographic zones, called “klappladser” (dumping sites). Material that meets the contamination thresholds may only be dumped inside these predefined areas.

These zones are mapped and managed spatially — and can be exported as KML files from public GIS systems, allowing for visual verification of whether vessels actually dump where they are allowed to, which this guide is about.

2. Tools and data sources

Here are the key tools and data types you’ll need:

AIS Data: Automatically broadcast by ships, includes vessel ID, position, speed, and sometimes draught (depth).
MarineTraffic or other shiptracking platforms: A global AIS visualization platform. The paid version allows you to upload custom zones and track multiple vessels, and that’s used in this case – this is the platform used in this guide.
KML Files: Polygon files from miljoegis.mim.dk, showing exact dump site boundaries.
Permit & Activity Reports: Permits are often publicly available. Activity reports are obtained via FOIA from the Danish Environmental Protection Agency (Miljøstyrelsen).
[Optional] Satellite images: Can add an extra layer of verification. However, they were difficult to obtain. Useful if sediment traces are visible.

3. Step-by-Step: How to monitor a dumping operation

This guide helps you detect whether ships dump material within their allowed zone — or outside it. It also shows recognizable patterns in dumping behavior.

Step 1: Identify ships

Use activity reports or search techniques (like Google Dorking) to find vessels authorized to dump. In MarineTraffic, many of these are categorized as “dredgers”, although not all — so you may need to combine different search techniques..

In Denmark, you must submit a FOI request to the Environmental Protection Agency (Miljøstyrelsen) for “klapstartindberetninger” (dump start notifications). Information should include:

Expected dumping start date
Dumping zone
Relevant permit
Vessel names and MMSI numbers

TIP: MarineTraffic’s paid version lets you create a fleet list. You can add all vessels from the activity reports and research under ‘Account → My Fleets’. Remember to use the MMSI number. It can look like this:

Step 2: Download the dumping zone

To verify whether a ship is dumping within a legal zone, you’ll need to find out whether the zones are publicly available.

In Denmark, they are. Visit miljoegis.mim.dk, click “Restriktive områder”, and click on “Klappladser” (dump zones). Use the arrow icon to the left and then the “T” (text selection tool) as shown below.

Then search for a specific dumping zone and click “Eksporter valgte rækker”. Be sure to export it as a KML file.

Step 3: Upload the zone to MarineTraffic

After downloading the KML file, upload it to MarineTraffic under Account → My Custom Areas. Click Create Custom Area → Import File → Browse Computer.

Edit the area once uploaded — color-code it so it stands out. For example, use green for all dump zones.

To view your areas on the map, open the menu on the right, and click Layers and show “My Custom Areas”.

Step 4: Search for the vessel and track it

Now you’re ready to track ships. Search for the vessel by name or MMSI number — this is the most reliable identifier. Click “Past Track” to see historical movements.

To match reported dumping dates, adjust the date range in Settings (in the playback bar below the map).

Alternatively, just follow vessels known for dumping practices in a given period and watch for suspicious patterns.

Step 5: Analyze behaviour

Once you’ve tracked a few vessels in MarineTraffic using AIS data and KML overlays, you’ll begin to notice recurring patterns in their behavior. Some ships may move in slow loops within a zone, pause repeatedly, or make multiple trips back and forth between a port and a designated dumping area. These patterns can indicate active dumping.

Here are a few common behavioural indicators to look for:

Slow circular or looping movement over the same coordinates
Speed consistently between 0–2 knots inside the dumping zone
Leaving and returning from the same harbor within short time spans
Repeating the same track multiple days in a row

OBS: The Danish authorities according to a report have described their classification method like this (this can also be to challenge):

“The current method relies solely on speed-filtered AIS data recorded at 5-minute intervals. Any vessel position with a speed of 0–2 knots within the dump zone is classified as potential active dumping, while all positions above 2 knots are defined as transit.”

When you know what patterns to look for, then you can check for signs of non-compliance:

Did the vessel operate outside the permitted zone?

Was dumping reported on a different date?

Is the zone mismatched with actual behavior?

4. Red Flags: How to spot suspicious activity

To sum up, be on the lookout for:

AIS gaps: Did the vessel’s signal disappear?
Stationary or slow position just outside the dump zone
Dumping patterns at locations with no listed permit

5. Verification

Once you’ve identified suspicious dumping behavior using AIS tracks and KML zones, the next question is: can you prove material was dumped?

While MarineTraffic does not directly confirm cargo status, two powerful methods can help verify whether a vessel was loaded or unloaded: vessel draught data and satellite imagery.

Method 1: Check the vessel’s draught (depth)

The draught tells you how deep the vessel sits in the water — in other words, how heavy it is. If the draught decreases during a trip, it may indicate that material was offloaded at sea.

TIP: In Denmark, all A-class ships (often dredging and dumping ships are in this category) are legally required to manually input their draught via their AIS transponder. This means you should be able to find this data.

How to get draught data:

You need to request for draught data at MarineTraffic. Email the MarineTraffic press office at press@marinetraffic.com — journalists often get access upon request.

Method 2: Cross-check with satellite imagery

Another method is to look for visual confirmation of dumping via Sentinel-2 or Landsat satellite images. In some cases, you can see sediment clouds or water discoloration after dumping.

However, matching a satellite pass exactly with the moment of dumping can be difficult due to:

Cloud cover
Timing mismatch
Limited resolution

In our investigation, we weren’t able to find matching imagery over Denmark. But in other regions or with better timing, this could provide direct visual evidence.

6. Visual example

DBB Asterix – Banedanmark permit

Operated for 62 days near Frederik IX’s bridge.
AIS-data from Marine Traffic showed repeated dumping patterns outside the allowed zone (see pictures below). On the 4th october 2023 it actually only made it halfway and turned around.

Notably, no draught data from Marine Traffic is available during this period — suspicious in itself.

7. Why KML-files matter

KML (Keyhole Markup Language) files are often overlooked in journalistic investigations. Yet, they are one of the most powerful tools for understanding where something happens — especially at sea, where legal boundaries and infrastructure aren’t visible on traditional maps.

KMLs are geospatial files that define precise polygons, lines, or points. When combined with ship movement data, satellite imagery, or other environmental overlays, they can reveal stories that would otherwise remain hidden.

How to track marine dumping with AIS and KML-files