Naturally,
again.

Baedari Lake, Banwol Lake, Haeoreum Lake and Jeonsocheon Stream. We record how all four change, year after year.

Baedari Lake Ongoing

Overview

Location · Jukbaek-dong, Pyeongtaek, Gyeonggi

A reservoir inside Baedari Eco Park in central Pyeongtaek. With almost no natural inflow, its level is kept up by pumping in treated water from a nearby sewage plant.

Water stays for a long time and urban runoff flows straight in when it rains, so fish kills, algae and odor have returned every summer.

Biovan's work

  1. 20262026 Fish kill prevention, Baedari Lake, Pyeongtaek2 photos ›
  2. 20252025 Fish kill prevention, Baedari Lake, Pyeongtaek6 photos ›
  3. 20242024 Fish kill prevention, Baedari Lake, Pyeongtaek15 photos ›
  • Since 2024, we have managed the site every spring to autumn to prevent fish kills. (2024 · 2025 · 2026 ongoing)
  • We monitor conditions before and after the warm-water season and continue microbe-based care.

Issue analysis

Stagnant water, dependent on inflow
The lake relies on treated sewage water, so when supply stops or the water warms, dissolved oxygen can drop sharply. The July 2021 fish kill happened when a supply outage coincided with high temperatures.
Eutrophication and excess aquatic plants
Nutrient buildup has been cited as the cause of overgrown weeds and algal blooms.
Direction of measures
A 2020 Pyeongtaek City study proposed total phosphorus treatment of the inflow, direct reservoir purification and circulation, and runoff reduction.

Related coverage

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Related coverage links to the original articles. Issue analysis is based on reported content.

Banwol Lake Ongoing

As reported

  • Grade IV → IIIWater quality improved
일간경기 · 2026.01.29 Read original ↗

Overview

Location · Daeya-dong, Gunpo, Gyeonggi

A reservoir in Daeya-dong, Gunpo, popular with residents for its lakeside trail.

Gunpo designated Banwol Lake a priority reservoir in 2020 and has continued water purification work since.

Biovan's work

  1. 20262026 Algae reduction & water quality, Banwol Lake, Gunpo
  2. 20252025 Algae reduction & water quality, Banwol Lake, Gunpo
  3. 20242024 Algae reduction & water quality, Banwol Lake, Gunpo
  4. 20232023 Algae reduction & changes, Banwol Lake, Gunpo4 photos ›
  5. 20222022 Banwol Lake site, Gunpo12 photos ›
  6. 20212021 Algae removal & water quality, Banwol Lake, Gunpo6 photos ›
  • Since 2021, we have carried out algae reduction and water quality work every year. (2021 · 2022 · 2023 · 2024 · 2025 · 2026 ongoing)
  • Site photos and records are on each project page.

Algae, before and after Same-spot comparison

  • Banwol Lake, year 1 (2021)Year 1
  • Banwol Lake, year 2 (2022)Year 2
  • Banwol Lake, year 3 (2023)Year 3

Photos taken from the same spot on the Banwol Lake trail.

Algae gone 2026 · same spot, before and after

  • Water by the deck · Late July
    Late July
    Water by the deck · Mid-August
    Mid-August

    Water by the deck

  • Water by the shoreline plants · Late July
    Late July
    Water by the shoreline plants · Mid-August
    Mid-August

    Water by the shoreline plants

Photos taken from the same spots in late July and mid-August 2026.

Issue analysis

Algae and bottom nutrients
With algae returning every summer, reducing the nutrients on the bottom that feed it has been a key task.
Watershed runoff
In 2023, Gunpo began a feasibility study on designating the Banwol Lake watershed a runoff management area.
Signs of recovery
According to reports, water quality improved from Grade IV to Grade III, and an otter — a natural monument — was spotted in January 2026.

Related coverage

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Related coverage links to the original articles. Issue analysis is based on reported content.

Haeoreum Lake Ongoing

Overview

Location · Nonhyeon-dong, Namdong-gu, Incheon

A lake in Haeoreum Lake Park, Nonhyeon-dong — an enclosed freshwater lake with no outside inflow. The nearby Neulsolgil Park lake, which was also renovated over stagnant water and poor quality, is included here.

Complaints about algae, turbidity and odor have continued for years.

Biovan's work

  1. 20262026 Algae prevention, Haeoreum Lake, Namdong-gu, Incheon (incl. Neulsolgil Park lake)
  2. 20252025 Algae prevention, Haeoreum Lake, Namdong-gu, Incheon (incl. Neulsolgil Park lake)
  • We began algae prevention in mid-2025 and are now in our second year. (2025 · 2026 ongoing)

Issue analysis

Limits of an enclosed lake
With no inflow, water sits for long periods and bottom sediment feeds the algae.
Repeated quick fixes
Algaecides, purifiers and fountains followed, but reports said they could not fix the root cause (June 2025).
Community involvement
In late 2022, civic groups, residents and the district office ran simple water tests together — local interest is high.

Related coverage

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Related coverage links to the original articles. Issue analysis is based on reported content.

Jeonsocheon Stream, Yeongjong Island 2021–2025

Overview

Location · Unnam-dong, Yeongjong-gu, Incheon (Yeongjong Island)

A small stream that rises east of Baegunsan on Yeongjong Island and flows through the Unnam district to the sea.

Housing development cut off its upstream source and household sewage flowed in, causing ongoing odor and water quality problems.

Biovan's work

  1. 20252025 Odor & water quality, Jeonsocheon Stream, Yeongjong-gu, Incheon6 photos ›
  2. 20242024 Odor & water quality, Jeonsocheon Stream, Yeongjong-gu, Incheon5 photos ›
  3. 20232023 Odor & water quality, Jeonsocheon Stream, Yeongjong-gu, Incheon6 photos ›
  4. 20222022 Odor & water quality, Jeonsocheon Stream, Yeongjong-gu, Incheon4 photos ›
  5. 20212021 Odor & water quality, Jeonsocheon Stream, Yeongjong-gu, Incheon6 photos ›
  • From 2021 to 2025, we handled odor and water quality work along Jeonsocheon Stream every year.
  • We continue to monitor the site and stand ready to respond whenever needed.

Before & after Same-spot comparison · 2021

Under the bridge

  • Under the bridge · Start of work, AprilStart · Apr
  • Under the bridge · JulyJul
  • Under the bridge · SeptemberSep

Photos taken from the same spots under the Jeonsocheon bridge and downstream.

Before & after Same-spot comparison · 2022

Under the bridge

  • Start of workStart
  • Midway through workMidway
  • End of workEnd

Photos taken from the same spot under the Jeonsocheon bridge.

Issue analysis

A stream with more visitors
Large cafés and restaurants have opened near the site over the past five years, drawing many more visitors. With more people around, the stream's odor and water quality directly shape the area's image.
Lost source, sewage inflow
Reports said stagnant water kept causing odor and insect complaints downstream.
Ecological restoration talks
In 2021, Jung-gu (now Yeongjong-gu) formed a public–private council to restore the stream, and a revised master plan went through review in 2024.
The task now
Odor and pollution were still being raised in 2026, with calls to both cut off pollution sources and keep up steady management. Related coverage ↗

Related coverage

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Related coverage links to the original articles. Issue analysis is based on reported content.