Õisu Järv
Viljandi, Estonia191 haView mapDirections
KAUR publishes the water-quality measurements for Õisu Järv. Here is what has been measured.
- 14 ft max depth
- Limited data
Õisu Järv in Viljandi, Estonia has official water-quality measurements, shown as reported. Water clarity: 1.5 m visibility. Phosphorus: 39.5 µg/L. Chlorophyll-a (algae): 17 µg/L. Maximum depth: 14.1 ft. Surface area: 471.7 acres.
How Õisu Järv is classified
Õisu Järv in Estonia is published with the authority's own measurements and class. The measurements here are published by the agency that samples the lake, as reported. Sampling here has recorded water clarity, phosphorus and algae (chlorophyll-a).
LakeQuality publishes no grade of its own beside it. Everything below thathas been measured is reported on this page.
Monitoring: the Estonian Environment Agency (Keskkonnaagentuur).
Õisu Järv is a 472-acre lake in Viljandi County, Estonia with a maximum depth of 14 feet.
Source: the Estonian Environment Agency (Keskkonnaagentuur) — not the EPA Water Quality Portal, last sampled 2025-09-15. Methodology: how these readings are compared.
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Õisu Järv is safe to swim in today is a call for the Estonian Environment Agency (Keskkonnaagentuur) and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Õisu Järv
These are the measurements KAUR publishes for Õisu Järv. More on the source.
Murky, only visible to about 4.8 ft. Phosphorus 39.5 µg/L. Chlorophyll-a 17 µg/L. TSI 57.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.45m | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 39.5µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 17µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 57 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
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Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
4.3 m
Surface area
191 ha
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Frequently asked questions about Õisu Järv
Where is Õisu Järv?
- Õisu Järv is a lake in Viljandi, Estonia. This page reports official water-quality measurements, shown as reported.
What is the water quality of Õisu Järv?
- Õisu Järv in Viljandi, Estonia has official water-quality measurements, shown as reported. Water clarity: 1.5 m visibility. Phosphorus: 39.5 µg/L. Chlorophyll-a (algae): 17 µg/L. Maximum depth: 14.1 ft. Surface area: 471.7 acres.
Is Õisu Järv safe to swim in?
- Õisu Järv has official nutrient and clarity measurements, not a bacteria swim class and not a safety clearance. Algal blooms, currents, and depth are not covered. Always check local notices before swimming.
How deep is Õisu Järv?
- Õisu Järv has a maximum depth of 14.1 feet. The lake covers 471.7 acres.
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Where this data comes from
36 measurements from 2 monitoring stations, 2019–2025. Retrieved from KESE / Estonian Environment Agency (not the EPA Water Quality Portal) on 2026-08-16.
Collected and reported by
- Estonian Environment Agency (Keskkonnaagentuur)
kese-ee36 samples · 2019–2025
Analytical methods
- KESE I-level monitoring
Monitoring station identifiers (2)
SJA1938000SJA1938003
Authority classifications are shown as the authority published them. See where the data comes from and data sources.