When Dissolved Oxygen Spikes
- Abi Croutear-Foy
- Apr 8
- 3 min read
What we learn from extreme values
Part 1: The Signal
A client recently asked whether dissolved oxygen (DO) values above 14 mg/L meant the sensor might be out of the water. It’s a fair question—extreme data points often raise red flags. But in this case, the data isn’t broken. It’s speaking.
And because we measure multiple parameters alongside DO—temperature, pH, turbidity, and conductivity—we can confidently say: the signal is real. And meaningful.
What we’re seeing is supersaturation. That’s when oxygen levels exceed 100% saturation—often a result of rapid photosynthesis by algae and aquatic plants, especially during long, warm summer days. This isn’t a sensor glitch—it’s a biological event.
As our Chief Scientist, Ebi Hussain, explains:
"Supersaturation is common for optical dissolved oxygen sensors in eutrophic systems over summer. The exaggerated daily fluctuations—peaks at mid-day, drops overnight—are the fingerprint of algal respiration and photosynthesis at play."
To put it simply:
"When oxygen levels spike during the day and drop sharply overnight in nutrient-loaded waterways, it’s not just natural variation. It’s the signature of algae dominating the system—a sign that the balance is tipping."
And while this photosynthetic activity is a key driver, it’s not the only factor. Supersaturation can be amplified by cold water (which holds more oxygen), low flow conditions, wind, riffles, and even changes in atmospheric pressure. It’s a multi-factor pattern—but one that can be read clearly when we see it in context.
That’s why we measure multiple parameters, not just DO. For example, when pH rises in lockstep with DO around midday and drops again overnight, it reinforces the photosynthetic signal. And if the sensor were truly out of the water, we’d expect flatlines in turbidity, pH, and conductivity—not the kind of dynamic diurnal data we’re seeing.
Finally, it’s worth noting: our confidence in the data is also underpinned by our process. We calibrate all AquaWatch DO sensors in 100% saturated water at 21°C near sea level. That means in real-world conditions—especially in cooler or higher-pressure environments—readings above 12 mg/L are both expected and accurate.
From an ecological perspective, we consider values above 9.1 mg/L to reflect full saturation under our standard calibration conditions. That’s part of how we ensure our systems remain defensible, transparent, and trusted.
Part 2: The System
Understanding what’s happening in our waterways isn’t just about detecting change—it’s about responding in time, with clarity and confidence.
That’s what SWIMS—our Strategic Water Intelligence & Management System—was built for. It’s not just sensors in the field or numbers on a screen. It’s a framework for decision-making, grounded in four key capabilities:
See Clearly – Our high-frequency sensors detected the DO spike in real time, supported by temperature, pH, turbidity, and conductivity data. The exaggerated daily swing in DO and pH pointed directly to biological drivers, not mechanical faults.
Act Early – With the pattern recognised—oxygen peaking at midday, dropping overnight—we were able to alert the client quickly, well before the issue escalated.
Share Insight – Using AquaVista, our AI-powered stream assessment tool, the client provided photos from the field. The visible algal blooms confirmed what the data was already telling us. This combination of real-time sensing and visual ground-truthing created a shared, confident diagnosis.
Prove Impact – The DO pattern identified here has now been folded into our alert logic. That means the next time it appears, the system will respond faster and more precisely. We don’t just capture events—we learn from them.
This is the strength of a connected system. Not just spotting issues, but turning them into opportunities to improve the health and resilience of our waterways over time.
Part 3: The Tool
We talk a lot about AI in environmental tech. But SWIMS is not a black box.
Yes, we use AI to speed up detection and uncover patterns sooner. But every result can be traced, explained, and defended. We believe tools should reflect the values they serve—transparent, thoughtful, and action-oriented.
SWIMS is our way of putting those values into practice. A system that helps people understand their water better, respond faster, and drive long-term improvement.
Insight without action is just awareness. Real impact comes when clarity leads to change.
Want to see how SWIMS could work in your catchment? Let’s talk. Whether you’re using our sensors or your own, we can help decode the signals and strengthen your response.
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