Hypoxia Maps - Summer 2025
Summer 2025 Hypoxia Monitoring
Hypoxia Monitoring Overview
The 2025 sampling schedule includes routine water quality surveys as well as summer-only hypoxia surveys.
Routine water quality surveys are conducted year-round, including during the summer months. During these surveys water samples are collected for from 17 stations and analyzed for nutrients and other water quality parameters. In addition, phytoplankton and zooplankton samples are collected from 6 stations in the Sound.
Hypoxia surveys are conducted during the months of June through September at an additional 30 stations. During hypoxia surveys, stations are sampled for dissolved oxygen to get a more accurate understanding of the extent of summer hypoxia conditions in Long Island Sound bottom waters.
DEEP's Long Island Sound Water Quality Monitoring Program utilizes data from both surveys to monitor the extent of low dissolved oxygen in Long Island Sound bottom waters, or 'summertime hypoxia'. Hypoxia condition maps are posted as soon as possible after each survey. Biweekly newsletters, summarizing the results of each survey, are also distributed to interested parties.
2025 Monitoring Results
Select a sampling date below to view the progression of hypoxia in the western Sound throughout the summer of 2025.
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Long Island Sound 2024 Algal Bloom Summary (Vol. 8, Issue 1)
June 2025:
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Water Quality Survey (WQJUN25) Summary (Vol. 8, Issue 2)
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WQJUN25 Dissolved Oxygen Distribution Map (June 2 - 4, 2025)
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Hypoxia Survey (HYJUN25) Summary (Vol. 8, Issue 3)
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HYJUN25 Hypoxia Map (June 17-18, 2025)
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Water Quality Survey (WQJUL25) Summary (Vol. 8, Issue 4)
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WQJUL25 Hypoxia Map (June 30-July 2, 2025)
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Hypoxia Survey (HYJUL25) Summary (Vol. 8, Issue 5)
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HYJUL25 Hypoxia Map (July 14-16, 2025)
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Water Quality (WQAUG25) Survey Summary (Vol. 8, Issue 6)
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WQAUG25 Survey Hypoxia Map (July 29- 31, 2025)
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Hypoxia Survey (HYAUG25) Summary (Vol. 8, Issue 8)
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HYAUG25 Survey Hypoxia Map (August 11 - 13, 2025)
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Water Quality Survey (WQSEP25) Summary (Vol. 8, Issue 8)
- WQSEP25 Hypoxia Map (August 25-28, 2025)
Dissolved Oxygen Distribution/Hypoxia Extent Maps Animation:
LIS Hypoxia Monitoring Distribution List
Interested in receiving future biweekly survey summary newsletters? Email Katie O'Brien-Clayton at Katie.OBrien-Clayton@ct.gov to be added to the distribution list.
LIS Monitoring Results and Annual Reports
Content last updated March 2026.