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 Bulgaria?

The median measured lake in Bulgaria reads 42 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 Bulgaria

Cleanest lakes in Bulgaria: 11 named lakes have an official total-phosphorus reading. The 11 below carry the lowest nutrient load — a measurement, not a LakeQuality A–F grade.

Lake map

Loading map…

Lowest phosphorus readings in Bulgaria

Phosphorus is the nutrient that feeds algae growth, so the lakes at the top of this table are the least loaded ones the Bulgaria monitoring programme has measured. The median measured lake in Bulgaria reads 42 µg/L.

Lake	Place	Total phosphorus	Chlorophyll-a	Secchi	Year
Dam Dospat	—	21 µg/L	—	4.5 m	2023
Tsonevo Dam	—	22 µg/L	—	4.0 m	2023
Dam Jrebchevo	—	27 µg/L	—	2.5 m	2023
Dam Batak	—	32 µg/L	3.0 µg/L	2.9 m	2023
Dam Koprinka	—	36 µg/L	15 µg/L	2.2 m	2023
Dam Topolnica	—	42 µg/L	7.4 µg/L	2.3 m	2023
Dam Kardjali	—	45 µg/L	—	3.3 m	2023
Dam Aleksandar Stamboliyski	—	46 µg/L	2.6 µg/L	3.0 m	2022
Dam Ivaiilovgrad	—	48 µg/L	4.9 µg/L	3.5 m	2023
Dam Studen Kladenec	—	48 µg/L	—	4.5 m	2022
Dam Ogosta	—	53 µg/L	11 µg/L	3.4 m	2023

Frequently asked questions

Which lakes in Bulgaria are the cleanest?: 11 named lakes in Bulgaria have an official total-phosphorus reading. This page ranks the 11 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 Bulgaria?: The median measured lake in Bulgaria reads 42 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.