Rain; eels; data centers; and more, in this week’s Potomac News Reservoir – Sept. 18, 2025 >>>

River Report: Rain Provides Some Drought Relief

Today’s U.S. Drought Monitor map shows a marked increase in drought conditions across the basin, with 19% in Severe Drought and 44% in Moderate Drought. However, the maps are released on Thursday with data ending on Tuesday, so this map does not take into account the 1+ inches the basin has received over the past 24 hours.

According to today’s ICPRB CO-OP Drought Monitoring report, the far western basin may receive up to 0.75 inches over the next day or so and an additional 0.0-0.25 over the next week.

The USGS gage at Point of Rocks is responding to the rain with a sharp increase in flow, currently above 2,400 cubic feet per second (cfs). A flow of 2,000 cfs is CO-OPs trigger for conducting Daily Monitoring with an email on precipitation conditions, water use, and other pertinent information to water suppliers and government agencies. As you can see in the graph, the flow is already starting to decrease. We will continue to monitor the conditions and provide updates on social media using #droughtmonitoring.

Reduce, reuse, and recycle… eel ladders

The American eel has historically been found throughout the Potomac River. Eels are an important part of the ecosystem, including as transport for larval freshwater mussels upstream. In recent centuries, dams and other hindrances have decreased access to available habitat, resulting in significantly reduced population numbers.

ICPRB is helping to restore the eels to their native range and make existing populations more resilient by installing eelways. These ladders help eels safely up and over a dam to expand their spawning area.

At Dam 5 (near Falling Waters, WV) along the North Branch Potomac River, this will be the second eelway. The first one was destroyed during a major storm some years ago. This left large pieces of metal in the river below the dam.

This week, ICPRB staff and our partners at U.S. Fish and Wildlife Service worked to remove the pieces of the first eelway. The remnants will be hauled to a machinist to be reconfigured into a eel ladder that will be designed to withstand strong storms and can be removed when the eels are not migrating.

See more pictures of the project (including videos of mussels and American eels!) on our recent Facebook post >>>

We would like to thank Mike Dudash at Eagle Aquatics, Inc. for letting us borrow the boat to haul the pieces.

This project is made possible through a grant from the National Fish and Wildlife Foundation with support from the U.S. Fish and Wildlife Service, USDA’s Natural Resources Conservation Service, the U.S. Forest Service and Altria. Additional support was provided by the National Park Service.

Back in Drought Monitoring; record dry August; mixed water quality results from CBP; and more, in this week’s Potomac News Reservoir – Sept. 4, 2025 >>>

River Report: CO-OP Initiates Drought Monitoring; September Water Supply Outlook

Due to low flows on the Potomac River, staff in ICPRB’s Section for Cooperative Water Supply Operations on the Potomac (CO-OP) began daily drought monitoring on Tuesday.

During active Drought Monitoring, CO-OP staff provide a daily email to stakeholders summarizing flow, weather, and demand conditions.

Join the conversation and find the daily drought monitoring information on Facebook using #droughtmonitoring.

Today’s US Drought Monitor Map shows 80% of the watershed in abnormally dry conditions.

The river’s flow at Point of Rocks USGS gage is 1860 cubic feet per second (cfs). Median for today is 2265 cfs.

Water Supply Outlook

The September Water Supply Outlook was published yesterday. This monthly report looks at the possibility of water supply releases from the area’s reservoirs based on data from current precipitation, river flow, forecasts, and more.

According to the report, despite a record dry August, there is a below-normal probability of needing releases from the Washington metropolitan area’s back-up water supply reservoirs for the remainder of the year.

Since last month’s Water Supply Outlook, the portion of the basin classified as abnormally dry has expanded from 0 to 38.5 percent (and has since jumped to 80%). The 12-month rainfall average is back in the negative at 1.5 inches below normal.

The Climate Prediction Center forecasts warmer-than-normal temperatures for September through November but noted no clear signal for precipitation amounts either way.

All that being said, the cooler, fall-like temperatures decrease evaporation as well as reduces the demand for water by both plants and people. This provides some relief from drought pressures when things get dry.

ICPRB will continue to monitor the situation and provide timely updates.

Registration Open for 2025 Potomac Conference on Harmful Algal Blooms

Join the Interstate Commission on the Potomac River Basin (ICPRB) on October 22 for a conference that will expound on the latest research, policy, and management of freshwater harmful algal blooms in the Potomac basin and beyond.

Click here for the full agenda >>>

The one-day conference will include sessions on HAB detection, benthic algal communities, case studies from local jurisdictions, and response strategies from different levels of government. A poster session will highlight additional research on the subject.

Registration is free.

Watersheds Highlighted at Regional Park

We’re excited to share that the City of Manassas will be using an ICPRB map in their Stormwater Education Trail at Dean Park, which is one of the largest parks in the city.

The sign, highlighting the Potomac River basin within the Chesapeake Bay Watershed, will be one of 11 other signs installed this fall.

The ICPRB Fourth Quarter Business Meeting is coming up on Tuesday, September 9, 2025. The meeting will be held in person at the offices of ICPRB in Rockville, Maryland. Commissioners will receive a welcome from Rockville Mayor Monique Ashton, honor outgoing Commissioners Tsai and McCabe, and learn about ICPRB’s work at the Chesapeake Bay Program. Find the draft agenda on our Business Meetings site on our webpage.

The public is invited to attend the meeting to provide public comment. Please contact us by Friday, September 5, for more information on how to attend.

Who owns the Potomac 🗺️; forever bugs🐛; flooding risk🌊; and more, in this week’s Potomac News Reservoir – August 14, 2025 >>>

A River Divided: Who Owns the Potomac River?

By Michael Nardolilli, Executive Director of the Interstate Commission on the Potomac River Basin

Why are the state boundary lines along the Potomac River so irregular? Why doesn’t the line run neatly down the middle of the river, as it does in many other states? The fascinating story behind the Potomac’s peculiar borders involves colonial land grants, centuries-old legal disputes, and evolving interpretations of land and water rights.

Ownership of the Potomac River was entangled in three conflicting colonial land grants that reflected the lack of knowledge about the watershed by the newly arrived inhabitants. In the early 1600’s, the Virginia Company received grants for Virginia, Maryland, and parts of Pennsylvania from King James I. Secondly, in 1632, Lord Baltimore was granted land in what is now Maryland to the Potomac River’s southern bank extending to the river’s “first fountain,” or its source. (This is the basis of Maryland’s claim to the entire Potomac). Finally, the area between the sources of the Potomac and Rappahannock rivers, known as the Northern Neck, was granted to Lord Fairfax.

So, the first step was to identify the “first fountain” of the Potomac among the many tributaries in its headwaters. Is the source of the Potomac River what we now know as North Branch Potomac (then known as the Cohaungoruton River)? Perhaps the South Branch? Or is it either the North Fork or South Fork of the Shenandoah? In 1736, Virginia sent a scouting party up the river to find the source. The surveyors chose the northernmost branch of the river, what we call the North Branch, which just happened to maximize the size of Virginia. Fairfax Stone was designated as the river’s source — and Maryland’s western boundary — setting the stage for centuries of boundary arguments.

In 1776, Virginia’s first Constitution ceded the river to Maryland, but reserved Virginia’s right to “free navigation and use of the river.” Maryland disputed Virginia’s claim, and the two states slapped tariffs on each other’s products that crossed the Potomac. In 1785, George Washington invited conferees from both states to Mount Vernon. There, the Compact of 1785 codified the right to toll-free travel along the Potomac.

Through many court cases, arbitrations, and legislation, the southern bank of the river became recognized as the boundary. The Black-Jenkins Award of 1877 declared the line would run from one headland to the next, not along the shore indentations. Land along the tidal Potomac would be set by the courts. Finally, in 1945, the Congress set the boundary line between DC and Virginia.

The Interstate Commission on the Potomac River is an interstate compact commission established by Congress in 1940. Its mission is to protect and enhance the waters and related resources of the Potomac River basin through science, regional cooperation, and education. Represented by appointed commissioners, the ICPRB includes the District of Columbia, Maryland, Pennsylvania, Virginia, West Virginia, and the federal government.

Find more about the history of the disputes in the Maryland State Archives or in this recent webinar recording, Who Owns the Potomac.

Forever Bugs

Yesterday, ICPRB staff joined environmental organizations from across the region to learn how to create “forever bugs” by preserving creek critters (known as benthic macroinvertebrates) in resin.

If you have ever visited our table at a festival, you have had the chance to say hello to a live creek critter. We use them for public education as they are an indicator of water quality. Unfortunately, there are times when we can’t collect live critters prior for an event, so these blocks of preserved bugs will serve as the next best thing.

See more photos on ICPRB’s Facebook page >>>

Join us at one of our upcoming festivals for a meet and greet with our creek critters:

• Sept. 13: In the Streets in Frederick, MD on Sept. 13

• Sept. 20: Rockville Science Center Community STEM Day

Thanks to the Fairfax County Stormwater team for sharing their knowledge and to the Montgomery County Department of Environmental Protection for organizing the event!