What the numbers mean
Our Lake Status page shows three numbers for each lake — Secchi depth, phosphorus, and chlorophyll-a. Here's what each one actually measures, what "good" looks like, and how to read a reading without a science degree.
Secchi depth (clarity)
What it is: How deep (in feet) a white disk stays visible as it's lowered into the water. Deeper = clearer.
How to read it:
- Higher is better. A lake that reads 10+ feet on a calm morning is a clear lake.
- Read the trend, not a single day. Wind, a recent rain, or a busy boating weekend will push a reading down. A one-day dip is normal; a season-long slide is a signal.
- Compare across lakes, not just across years. Koonz and Beaulieu have different baselines; a number that's "low" on one may be normal on the other.
Phosphorus (nutrient level)
What it is: The concentration of phosphorus in the water, in parts per billion (ppb). Phosphorus is the nutrient that most often limits algae growth in lakes — lower is better.
How to read it:
- Lower is better, always. There's no "high is good" case for phosphorus in a lake.
- Tie it to the season. Phosphorus is often highest in late spring/early summer (post-turnover release from sediment) and can dip through the stratified summer.
- Tie it to the trend. A one-year spike can be weather; a three-year climb is a loading problem, and that's where the Association's work (runoff, fertilizer, septic) kicks in.
- Context, not a single threshold. "Good" varies by lake size, depth, and trophic status. The water-quality report shows the history so you can see where our lakes sit relative to their own past.
Chlorophyll-a (algae proxy)
What it is: A lab measurement of chlorophyll-a, the green pigment algae use to make food from sunlight. It's a proxy for how much algae is currently in the water — higher means more algae.
How to read it:
- It's the "right now" number. Chlorophyll-a reflects the current algal population, which is why it swings with weather and blooms.
- Read it with Secchi, not alone. A high chlorophyll with a low Secchi is a bloom; a high chlorophyll with a decent Secchi might be a benign, well-mixed green week.
- Watch for the die-off. After a bloom, chlorophyll drops but dissolved oxygen can also drop as the dead algae decomposes. That's why we keep sampling for a couple of weeks after a visible bloom ends.
How to read a reading like a member
When a new reading lands, the useful questions are:
- Which lake? Koonz and Beaulieu are different lakes; compare each to its own past.
- Compared to when? A single number is a snapshot. Compare to last month, last year, and the season's trend.
- What's the weather been doing? Wind, rain, and a hot stretch explain a lot of short-term variation.
- Is it one number or a pattern? One odd Secchi is noise. Three readings in a row trending the same way is a conversation.
- Does it match what you're seeing? If the numbers say "clear" and the lake looks green, that's worth a report — the field and the lab should agree.
Where to see the full picture
The water-quality report has the full history, yearly averages, and both lakes side by side. That's the page to open when you want to judge the trend rather than a single reading — and it's the page the board uses to decide where to focus the Association's effort next.
A note on scale
None of these numbers are "pass/fail." A lake isn't graded A-to-F on a Secchi depth. What we're watching is the direction of travel over a season, a year, and a decade. A slow, steady improvement is a win even if no single number looks dramatic. A slow, steady slide is a problem even if no single number looks alarming. That's the whole point of monitoring.