North Bar Lake Water Quality Trend

Reading North Bar Lake's trajectory

Across 5 years of sampling, North Bar Lake's overall water quality holds steady. Stable trends are the most common pattern and the easiest to misread — they don't mean the water is clean (a chronically impaired lake can hold steady at impairment), nor do they mean the water is fine (it can hold steady at "marginal"). Read the trend alongside the current Grade and the §303(d) listing rather than in isolation.

A 5-year sample window is enough to surface directional trends but short enough that one or two unusual weather years can still influence the read. Use the trend as a signal, but combine it with the most recent absolute Grade rather than relying on direction alone. The state environmental agency's lake-specific monitoring reports often add context that a five-year trend line by itself can't carry.

Clarity (Secchi depth), phosphorus, and chlorophyll-a are the three metrics most consistently sampled across years and most useful as trend indicators. Clarity captures the visible signal — how deep you can see into the water. Phosphorus is the primary nutrient driving algal growth in most lakes. Chlorophyll-a measures algal biomass directly. Together they describe the same underlying water-quality state from three angles; when all three agree on direction, the trend signal is strong.

How to read this

• Clarity (Secchi depth): deeper visibility is better. An upward line means the water is getting clearer.
• Phosphorus & Chlorophyll-a: lower is better. A downward line means fewer nutrients fueling algae growth.
• Year-to-year variability is normal. Weather, sample timing, and short-window data all add noise. Look at direction, not single-year jumps.

Methodology

Each metric is calculated from EPA Water Quality Portal samples. Annual values are the median of all samples taken that year. The trend direction comes from a linear regression of those annual medians; we classify it as improving, declining, or stable when the change-per-year is below 2% of the long-run mean. The current cache spans roughly 2020–2024, which is a short window for climate-scale claims. Use this page to spot direction and as a launch point — link out to the EPA WQP for the raw record before citing as evidence.