Secchi Disk project

You can participate in this project by making a Secchi Disk (a 30 cm flat white disk attached to a tape measure or rope, see the project website for more details) and using the free to download ‘Secchi’ application to record your measurements and upload them to the database; the Secchi app is available for iOS, Android and Windows devices from the iTunes, Google Play and Microsoft stores.

Once uploaded, your data should appear on the map below within 48 hours.

The long-term aim is to understand more about the phytoplankton (microscopic, plant-like cells) that underpin the marine food chain.

Define search boundary
Limit by boat
Free Search
Radius around Free Search
Show Clustering
Secchi Legend
Secchi Depth
> 0m
Secchi Filter Help

Welcome to Secchi Filter Help

This information is to help you navigate the filter and the operation of the map. The map shows markers where a Secchi reading has taken place. In some cases there are multiple readings from the same location.


Each marker represents a boat (or reading). Some markers may not have a boat name associated with them if the owner did not provide that information.

Clicking on a marker will show you the information for that marker, any associated media, and a and a graphical representation of the data as a bar chart for either the boat associated with the marker, or all the markers within the boundary (on a boundary search), or all the markers returned by the filter.


Each bar chart represents the data associated with either a filter search or an individual marker on the map. All filters are applied to the bar charts as they are for the markers.

You can change the information and media shown by clicking on an entry on the chart.


Selecting to cluster will aggregate the icons on the map into groups and show you a count of all the icons within the group. Clicking on a cluster will enable you to drill down into that cluster and show you, were applicable, all uniquely located markers. If the cluster does not show you individual markers upon a click, it will mean there are multiple makers at the same location.

Boat name

Selecting a boat name from the drop down list provided on the map will automatically restrict all searches to include the boat name - unless you uncheck the 'Limit by boat' option on the filter.

Boundary Search

The boundary search allows you to define a search area on the map and apply a filter to narrow your results. The boundary search will not include the Free Search (and therefore the radius and units) but will include all other search parameters.

To use this feature you need to select the checkbox and click on the map. This will show you a placemark that you can drag around the screen to define your boundary (the geo-fenced area).

Once the geo-fenced area is defined you can either set other filter options or click the filter button to return the results of your search, which will appear as markers on the map. (Please refer to the legend to distinguish between markers.)

Filter Options

  • DEPTH: allows filtering on the Secchi depth that was recorded. You can filter further by selecting a comparison operator to apply to the Secchi depth reading.
  • FROM DATE: defines the start date of a date period to search
  • TO DATE: defines the end date of a date period to search

Free Search

Performing a free search with the default filter (or any current filter) will place a marker at the location found and show you the markers for the readings near that area. All other results are still visible if you zoom out of the map.

Free search allows you to select a place on Earth, and a radius around that place (measured in the units you chose), to filter readings when you click on the filter button. (Please note that if a Boundary Search is defined this will be ignored.)

Enter a Location

Type a name of a location, for instance Davie Straight, and click Find. A marker will appear on the map to indicate the location you chose. If you have searched previously, or you have left the filter blank, and you then zoom to a location, the map will show markers from readings that are within the boundary of the map.

To search for recordings near this location, select your unit and define your radius and click on the Filter button.


The units you can define are either Kilometers, Miles or Nautical miles, depending on your preference.

Radius Dial

Click on the dial to move the marker and define a radius in the units you chose. The radius uses a haversine calculation to define the circle around the location and will return all filter entries that fall within that boundary.

Secchi Information
Boat name:
Location Name:
Secchi Depth: