Limitations
What AquaLens can and can't tell you.
It reads the colour of water from space. That is useful, and it has limits.
Does Low mean the water is clean?
No. From space AquaLens sees algae, mud and floating plants. Bacteria, parasites, toxins and dissolved chemicals are invisible to a satellite; only a water sample finds them.
Does it detect algae toxins?
No. It sees the green of algae, which often comes before toxins. A bloom it flags still needs a lab test to say whether it is toxic.
How old is the photo?
Sentinel-2 passes about every five days, and cloud can hide the water, so the newest clear photo can be a week or two old. Every result shows its date.
Can it check small ponds and narrow rivers?
Only where it sees at least half a hectare of clear water (about 70 by 70 metres). Water next to the shore mixes with the land, so small or narrow water is read less surely, and the result says how sure it is.
Why can a lake read High one month and Low the next?
On very clear, dark water the algae signal is faint, so a small difference in how each photo is corrected for haze can move the reading a long way. The open water of Lake Titicaca's Puno Bay read High, Low, High and Low in four photos in 2026 while its inner bay read the same each time. Look at several months together, and trust a lab sample over any single photo.
Can it replace water testing?
No. It tells you where a test would tell you most, so a limited lab budget goes further.
Who decides whether water is safe?
The people responsible for the water, under local rules. AquaLens gives advice, not a certificate.