State water-quality picture · #46 by reported lake-type waterbodies
Maryland lakes and reservoirs
Every figure on this page is computed from the assessment decisions Maryland reported to the U.S. Environmental Protection Agency under Clean Water Act sections 303(d) and 305(b) (reporting cycles 1996–2024), plus daily water-level observations from the U.S. Geological Survey.
- 63
- Reported waterbodies
- 32
- Not supporting a use
- 11
- Fish use not supporting
- 1
- Gauged lake
Maryland in one line
63 lake-type waterbodies in Maryland are reported to EPA ATTAINS across reporting cycles 1996–2024: 32 assessed as not supporting at least one designated use, 18 fully supporting, and 13 without a definitive overall verdict. The most-listed impairment cause is Phosphorus, Total, on 21 waterbodies.
- 63
- reported waterbodies
- 32
- not supporting a use
- 18
- fully supporting
- 64%
- of definitive verdicts impaired
An unassessed waterbody is neither confirmed clean nor confirmed impaired; states assess on multi-year cycles.
Maryland's smaller reported lake-type inventory
At 63 units, Maryland is in the lowest third of state lake-type registers. The charts below describe that compact filing set, not a national-scale inventory.
Data updated 2026-08-17
According to the U.S. Environmental Protection Agency's ATTAINS program, Maryland reported 63 lake-type waterbodies in Maryland in the August 2026 extract. See our methodology for filer attribution and multi-year reporting cycles.
Overall-status split on Maryland's compact register
Every reported lake-type unit in this smaller Maryland filing set falls into exactly one overall-status bucket. The bar partitions 63 units; cause and gauge panels below stay separate.
Most-listed impairment causes in Maryland
Waterbodies carrying each listed cause, most first
- Phosphorus, Total
Phosphorus, Total
21 waterbodies
- Sedimentation/Siltation
Sedimentation/Siltation
11 waterbodies
- Mercury in Fish Tissue
Mercury in Fish Tissue
9 waterbodies
- Chlorophyll-a 6
Chlorophyll-a
6 waterbodies
- PCBs in Fish Tissue 2
PCBs in Fish Tissue
2 waterbodies
What this shows Phosphorus, Total is the most-listed impairment cause in Maryland, on 21 of the lake-type waterbodies reported there.
Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.
Maryland: 64% of ruled verdicts are not-supporting, against a national share of 53%, 1.2× the national rate.
Reporting practice
How much of the Maryland inventory carries a definitive verdict
Each reporting authority decides how much of the water it files to EPA it actually assesses in a cycle. That decision sets the denominator behind every count on this page.
Maryland holds the 46th-largest reported lake-type inventory in the country, 63 assessment units, carrying a definitive verdict on 79.4% of it. The counts above describe the 50 units carrying a verdict, not all 63 reported. Maryland has also retired 2 lake-type assessment units, superseded filings that are kept on the site but not counted here.
The states reporting at the nearest rates are Arkansas (81.3%) and Nevada (76.8%).
Assessing more of an inventory is a reporting choice, set by cycle length, monitoring budget and how finely a state splits its waters into units. It is not a measure of water quality, and it is why a raw count from one state does not sit beside a raw count from another. How assessment coverage varies.
Maryland against every comparable state
Share of reported lake-type waterbodies carrying a definitive verdict
79.4% 19th of 47 higher than 28 of 47 states
the 47 comparable states, by definitive-verdict share
Each bar is a band; taller bars hold more states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA ATTAINS · Reporting cycles 1987–2026
Each bar counts states whose definitive-verdict share falls in that 10-point band. The 47 states shown are those reporting at least 25 lake-type units; a share off a smaller inventory is precision the data does not have.
By size
Largest assessed lakes in Maryland
By assessed acreage as reported in ATTAINS. Acreage is the assessed unit's size, which can differ from a lake's full surface area.
| # | Waterbody | Assessed acres |
|---|---|---|
| 1 | Deep Creek Lake Not Supporting | 3,887 |
| 2 | Conowingo Reservoir Not Supporting | 3,070 |
| 3 | Liberty Reservoir Not Supporting | 2,933 |
| 4 | Loch Raven Reservoir Not Supporting | 2,236 |
| 5 | Prettyboy Reservoir Not Supporting | 1,472 |
| 6 | Jennings Randolph Reservoir Fully Supporting | 941 |
| 7 | Youghiogheny River Lake Not Supporting | 788 |
| 8 | Rocky Gorge Reservoir Not Supporting | 627 |
| 9 | Triadelphia Reservoir Not Supporting | 570 |
| 10 | Little Seneca Lake Fully Supporting | 480 |
| 11 | Savage Reservoir Not Supporting | 325 |
| 12 | Piney Run Reservoir Not Supporting | 301 |
By cause count
Most-listed waterbodies in Maryland
Waterbodies carrying the most listed impairment causes among the lake-type units reported by Maryland.
| # | Waterbody | Listed causes |
|---|---|---|
| 1 | Clopper Lake Not Supporting | 3 |
| 1 | Centennial Lake Not Supporting | 3 |
| 1 | Conowingo Reservoir Not Supporting | 3 |
| 4 | Adkins Pond Not Supporting | 2 |
| 4 | Big Mill Pond Not Supporting | 2 |
| 4 | Broadford Lake Not Supporting | 2 |
| 4 | Higgins Mill Not Supporting | 2 |
| 4 | Lake Lariat Not Supporting | 2 |
| 4 | Lake Linganore Not Supporting | 2 |
| 4 | Liberty Reservoir Not Supporting | 2 |
Every row in this table ties with at least one other on the ranked value: 3 at 3 (rank 1), 7 at 2 (rank 4). Tied rows share a rank and are listed in no meaningful order; where a tie reaches the top the medal is shared, because nothing separates those rows.
Gauge network
Lakes with a daily level record in Maryland
Lakes with a linked USGS gauge and a daily water-level record. Readings are daily-batch snapshots, not real-time.
States with similar inventory scale or impairment load
Two EPA ATTAINS peer sets outside Maryland. The reporting-practice chart above stays on definitive-verdict share; these neighborhoods are cross-state nearest neighbors on register size and not-supporting counts.
States with a similar reported inventory
Nearest states by lake-type units on the register (63 here).
Comparable not-supporting counts
Nearest states by units assessed not supporting a use (32 here). Inventory peers above are omitted.
- Maine · 31 not supporting · 1 off
- Arizona · 34 not supporting · 2 off
- Delaware · 40 not supporting · 8 off
- Connecticut · 44 not supporting · 12 off
Peers are nearest-neighbor matches on EPA ATTAINS register size and not-supporting counts among states with at least 25 reported units. Impairment peers skip states already listed in the inventory column so the two link sets stay distinct.
Using this state picture
- Comparisons across states hold on shares, not counts: 79.4% of the inventory reported from Maryland carries a definitive verdict, 19th of 47 comparable states. National rankings
- Fish-consumption verdicts here are assessment decisions. Species-level meal advice comes from the state fish-advisory program. Consumption guide
- Browse every named Maryland waterbody with a populated record. Browse waterbodies
PlainLakes renders state assessment decisions and federal gauge observations without modification.
Figures on this page are computed from the assessment decisions Maryland reported to EPA's ATTAINS system and from USGS National Water Information System daily values, no number is typed in by an editor. State counts aggregate every lake-type assessment unit reported by Maryland, including unnamed units that never receive their own page. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-08-17. Primary sources: EPA ATTAINS and USGS National Water Information System.