Mini-secchi disk

Measure water transparency, colour and pH with the mini-Secchi disk: a handheld device that is easily deployed from shore or boat.

Availability: Currently in development
Developer: Brewtek (with Plymouth Marine Laboratory)
Contact: Brewtek:
Approximate cost: The mini-Secchi disk can be provided with a range of options. The basic mini-Secchi disk package includes a mini-Secchi disk and spare components. The current cost for an individual purchase using 3D-printed manufacture is between £85 - £95, depending on whether you would like a mini-Secchi disk (10 m tape) or midi-Secchi disk (20 m tape). For bulk purchase discounts may apply. We are also investigating other manufacturing methods to reduce costs further.  See for more information. 


  • Dimensions: 13 x 10 x 5 cm when fully compacted.
  • Power requirement: None
  • Method to transmit data: A mobile app has been developed to calculate Secchi disk depth, record photos and additional observation data and submit readings to a database.
  • Deployment method: Citizen scientists can deploy from the shore or a boat.


Secchi disk measurements have been used to record water transparency over hundreds of years, and are used as a proxy for eutrophication in international water quality monitoring programmes. Recently, a simple hand-held device was designed to measure the Secchi depth and water colour (Forel-Ule scale) of lake, estuarine and nearshore regions. The device is manufactured with marine resistant materials (mostly biodegradable) using a 3D printer and basic workshop tools. It is inexpensive to manufacture, lightweight, easy to use, and accessible to a wide range of users. It builds on a long tradition in optical limnology and oceanography, but is modified for ease of operation in smaller water bodies, and from small watercraft and platforms.
As part of ongoing development, MONOCLE has partnered with Brewtek, who designed the device, to provide further support for enhanced data flows and analysis. A new mobile App is designed to collect photos and the disk has been expanded with a clip to attach pH paper.
The 3D-printable design is particularly useful in community, educational and hobbyist settings.
For larger projects, mass-manufacturing is desired and this is currently being set up, with the first units expected to be available mid-2022.

What does it measure?

  • Water transparency
  • Colour
  • pH

How does it work?

The disk is lowered from a jetty or boat. Using an integrated measurement tape on a spindle, precise readings of the maximum visibility depth of the disk can be recorded. With the disk at half the visibility depth, the user is requested to estimate water colour using the Forel-Ule scale which is attached to the spindle. Additional observations of pH and surface water colour can be recorded through the app. The disk has an ultra-compact design and easily fits in a backpack to take on excursions in nature. In windy conditions additional weight can easily be added to the disk.

  • High portability
  • Easy deployment and storage
  • Assess water colour, transparency and pH using a single device
  • Contribute to image analysis by submitting photos through mobile App

Image gallery

Deployment information

Citizen scientists can deploy from the shore or a boat.

Instructional video

Standardised data access

We provide several interoperable data interfaces, as detailed below:

Mini-secchi disk data is owned by Plymouth Marine Laboratory and DDQ and available in WMS and WFS formats:

WMS GetCapabilities
WFS GetCapabilities

Documentation and publications

Supporting materials

User guide: Deploying the mini-secchi disk (PDF 1.4MB)
Video: How to deploy a Mini-Secchi disk
Download App in the Google Play store
Download App in the Apple store

Download the operational protocols for MONOCLE sensors and platforms
This document provides a set of protocols for the deployment of MONOCLE systems to ensure best practices to collect reliable data.
System user and developer handbook

This handbook provides an overview of the data requirements and interfaces that were adopted in the sensors and observation platforms of MONOCLE.

Sensor deployment activity

The data below shows recent sensor deployment activity. Access more detail and explore other sensor deployment activity on the MONOCLE dashboard .

Other sensors and platforms

Measure water transparency with a low-cost sensor that you can build! Advanced KdUINO sensors also detect optical and temperature stratification in the water column.

FreshWater Watch (FWW)
A methodology for Citizen Scientists to use sensors to investigate the health of the world’s freshwater ecosystems.

Hyperspectral Radiometer for Global & Diffuse Irradiance (HSP1)
A novel sensor to accurately measure the spectrum of sunlight near the water’s surface

Water Insight SPectrometer Station (WISPstation)
Measure water reflectance and key water quality parameters fully autonomously, emission-free, without any chemicals, at a high frequency and get results available near-real-time

MapEO Water
Using state-of-the art drone technology to monitor water quality. The MapEO Water service converts drone data into geo-referenced images providing information on the physical properties of water bodies.

Take quick and easy ocean colour measurements using this low-cost add-on for your smartphone.

Solar tracking radiometry platform (So-Rad)
Control and automate underway radiometric measurements for satellite validation from ships and buoys