DOI: 10.5061/dryad.dfn2z35fj
title: Data from: Cities can grow without harming lakes: Lake Washington has become less eutrophic despite rapid population growth

description: As cities grow, lakes are often assumed to suffer from increasing nonpoint
 pollution. Many waterbodies have become more eutrophic in recent decades,
 as expected, but many others have become less eutrophic, especially in
 urban/suburban areas. What policies, practices, and ecosystem processes
 have helped some lakes stay stable or become less eutrophic even in a
 growing city? Identifying and understanding success stories is important
 to continue protecting these lakes and improving other urban/suburban
 lakes. We found one such success story when we examined water-quality
 trends over the past 25 years (1998–2022) in Lake Washington, a
 well-studied large lake in the Seattle metro area. The watershed
 population grew rapidly during that time (34% from 2000–2020), yet Lake
 Washington became substantially less eutrophic, and indicators of
 development impacts stabilized or decreased. Chlorophyll concentrations
 during the main spring bloom decreased sharply ( 25%/decade), and water
 clarity and near-bottom dissolved oxygen both increased (8.5% and
 17%/decade, respectively). Alkalinity and specific conductance had
 increased during the 1970s–1990s, but in recent decades they have held
 stable. Peak winter/spring nitrogen and phosphorus concentrations
 decreased (-4.9% and -5.6%/decade, respectively), indicating decreased
 watershed inputs. The type of development during this time was likely a
 key contributor: we found no net loss of forest area and little increase
 in developed land area (4.7% from 2001–2021). Instead of expanding into
 new areas, redevelopment increased density on already-developed land and
 likely drove improvements in stormwater treatment and other environmental
 protections. Future work comparing stream watersheds could help discern
 which specific aspects of redevelopment helped reduce nutrients and other
 impacts. However, nutrient reductions were not the only factors
 controlling the lake’s trophic state; chlorophyll decreased much more
 strongly than phosphorus did. Lake Washington is a complex ecosystem
 governed not only by water chemistry but also by interactions with
 physical and biological factors such as stratification, warming,
 phytoplankton community shifts, or food-web interactions. A better
 understanding of all these factors is essential to provide sound
 scientific guidance and ensure that Lake Washington and other lakes can
 thrive in a growing city.
description: # Data from: Cities can grow without harming lakes: Lake Washington has
 become less eutrophic despite rapid population growth Dataset DOI:
 [10.5061/dryad.dfn2z35fj](10.5061/dryad.dfn2z35fj) ## Description of the
 data and file structure This contains the water-quality data associated
 with the following manuscript: Nidzgorski, Daniel A. and DeGasperi, Curtis
 L. (2025). Cities can grow without harming lakes: Lake Washington has
 become less eutrophic despite rapid population growth. Ecosphere. For
 questions or requests, please contact Daniel Nidzgorski at
 [dnidz@civiceco.org,](mailto:dnidz@civiceco.org) and we would appreciate
 it if you cited. ### Files and variables #### File:
 LakeWashingtonWaterQuality1998-2022.csv **Description:** These
 water-quality data were collected from Lake Washington (Seattle area, USA;
 47.6° N, 122.3° W) by King County's long-term monitoring program.
 This dataset includes data from 1998-2022 from the Madison Park 0852
 monitoring location at one of the deepest points in the lake (~65 m deep).
 All missing data represented as NA. ##### Variables * Locator: Numeric
 designator for the sampling location * Site: Name of the sampling location
 * LabSampleNum: Unique sample ID number generated by the King County
 Environmental Lab. * CollectDate: Sample collection date * Depth: Depth
 (in m). NAs indicate missing values, usually for chlorophyll samples that
 were collected as an integrated sample from 0-10 m. * Parameter: Parameter
 name. "Field" indicates parameters measured in situ with field
 instruments rather than by collecting water samples for lab analyses. *
 Value: Measured value of that parameter for that sample. NAs indicate
 missing values, usually because the concentration was less than the method
 detection limit (