Why rank lakes by phosphorus?

Phosphorus is usually what limits how much algae a lake can grow, so it is the earliest signal that a lake is under nutrient pressure. It is also the measurement these agencies publish most consistently, which makes it the fairest way to compare lakes across a country.

Is a low-phosphorus lake safe to swim in?

Not necessarily. A lightly loaded lake can still carry bacteria, a seasonal algal bloom, or contaminants that a nutrient reading does not cover. Check the local authority notice for the day you plan to go.

What is a typical phosphorus level in Finland?

The median measured lake in Finland reads 17 µg/L of total phosphorus. Lakes below roughly 10 µg/L are considered nutrient-poor and usually run clear; above about 30 µg/L a lake is generally nutrient-rich and more likely to green up in summer.

Cleanest lakes in Finland

Cleanest lakes in Finland: 3,997 named lakes have an official total-phosphorus reading. The 20 below carry the lowest nutrient load — a measurement, not a LakeQuality A–F grade.

Lake map

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Lowest phosphorus readings in Finland

Phosphorus is the nutrient that feeds algae growth, so the lakes at the top of this table are the least loaded ones the Finland monitoring programme has measured. The median measured lake in Finland reads 17 µg/L.

Lake	Place	Total phosphorus	Chlorophyll-a	Secchi	Year
Harrijärvi	Inari	3.0 µg/L	1.1 µg/L	11 m	2023
Iso Kuokkajärvi	Puumala	3.0 µg/L	2.4 µg/L	5.3 m	2025
Iso Polvijärvi	Liperi	3.0 µg/L	2.7 µg/L	6.0 m	2021
Kalettomanjärvi	Mäntyharju	3.0 µg/L	1.0 µg/L	5.0 m	2026
Karijärvi	Kouvola	3.0 µg/L	2.9 µg/L	5.0 m	2025
Katriinajärvi	Inari	3.0 µg/L	1.7 µg/L	3.5 m	2026
Kilpisjärvi	—	3.0 µg/L	1.2 µg/L	7.2 m	2026
Korpijärvi	Mäntyharju	3.0 µg/L	2.0 µg/L	4.9 m	2024
Mykrä Lake	Puumala	3.0 µg/L	1.8 µg/L	4.8 m	2025
Nitsijärvi	Inari	3.0 µg/L	1.6 µg/L	5.3 m	2023
Pahakala Lake	Liperi	3.0 µg/L	8.1 µg/L	5.6 m	2018
Pitkä Surnujärvi	Inari	3.0 µg/L	1.9 µg/L	5.0 m	2023
Rahajärvi L. Raahajävri	Inari	3.0 µg/L	1.6 µg/L	5.5 m	2026
Särkilampi	Mikkeli	3.0 µg/L	—	1.8 m	2023
Särkkäjärvi	Ilomantsi	3.0 µg/L	1.0 µg/L	10 m	2023
Sevettijärvi	Inari	3.0 µg/L	1.8 µg/L	6.3 m	2026
Sierramjavri Lake	Inari	3.0 µg/L	1.5 µg/L	5.0 m	2026
Sonnanen Lake	Heinola	3.0 µg/L	1.3 µg/L	9.4 m	2026
Kuivajärvi	Mikkeli	3.1 µg/L	—	—	2020
Kuorinka Lake	Liperi	3.1 µg/L	1.5 µg/L	7.5 m	2025

Showing 20 of 3,997 named lakes. Open a county or place page for the rest.

Frequently asked questions

Which lakes in Finland are the cleanest?: 3,997 named lakes in Finland have an official total-phosphorus reading. This page ranks the 20 lowest. Phosphorus is the nutrient that feeds algae growth, so a low reading means a lightly loaded lake — it is not a swim-safety class and not a LakeQuality A–F grade.
Why rank lakes by phosphorus?: Phosphorus is usually what limits how much algae a lake can grow, so it is the earliest signal that a lake is under nutrient pressure. It is also the measurement these agencies publish most consistently, which makes it the fairest way to compare lakes across a country.
Is a low-phosphorus lake safe to swim in?: Not necessarily. A lightly loaded lake can still carry bacteria, a seasonal algal bloom, or contaminants that a nutrient reading does not cover. Check the local authority notice for the day you plan to go.
What is a typical phosphorus level in Finland?: The median measured lake in Finland reads 17 µg/L of total phosphorus. Lakes below roughly 10 µg/L are considered nutrient-poor and usually run clear; above about 30 µg/L a lake is generally nutrient-rich and more likely to green up in summer.