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 Spain?

The median measured lake in Spain reads 15.1 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 Spain

Cleanest lakes in Spain: 12 named lakes have an official total-phosphorus reading. The 12 below carry the lowest nutrient load — a measurement, not a LakeQuality A–F grade.

Lake map

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Lowest phosphorus readings in Spain

Phosphorus is the nutrient that feeds algae growth, so the lakes at the top of this table are the least loaded ones the Spain monitoring programme has measured. The median measured lake in Spain reads 15.1 µg/L.

Lake	Place	Total phosphorus	Chlorophyll-a	Secchi	Year
Embalse Del Negratín	Andalucía	6.5 µg/L	0.60 µg/L	—	2017
Embalse Barrendiola	Gipuzkoa	10 µg/L	1.1 µg/L	3.2 m	2025
Embalse Ibiur	Gipuzkoa	10 µg/L	1.1 µg/L	3.8 m	2025
Urkulu Embalse	Gipuzkoa	10 µg/L	0.90 µg/L	3.0 m	2025
Embalse Albina	Araba/Ãlava	12 µg/L	0.50 µg/L	1.9 m	2025
Embalse Del Jándula	Andalucía	14 µg/L	1.5 µg/L	—	2017
Ibaieder Embalse	Gipuzkoa	16 µg/L	1.4 µg/L	4.6 m	2025
Embalse de Colomera	Andalucía	20 µg/L	1.7 µg/L	—	2017
Embalse Ullibarri	Araba/Ãlava	26 µg/L	2.3 µg/L	3.1 m	2025
Embalse Aixola	Gipuzkoa	35 µg/L	0.40 µg/L	5.5 m	2025
Embalse Urrunaga	Araba/Ãlava	35 µg/L	0.30 µg/L	3.4 m	2025
Embalse de Cubillas	Andalucía	38 µg/L	14 µg/L	—	2017

Frequently asked questions

Which lakes in Spain are the cleanest?: 12 named lakes in Spain have an official total-phosphorus reading. This page ranks the 12 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 Spain?: The median measured lake in Spain reads 15.1 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.