Early results and lessons learned from biomanipulation and chemical restoration of a eutrophic shallow lake

Introduction Over 44% of European lakes fail to meet ecological quality standards, prompting substantial investment in lake restoration to achieve good ecological status. Unfortunately, effects are often short‐lived due to persistent internal phosphorus (P) loading and strong cyprinid‐driven bottom‐up control, which limits water quality improvements and suppresses top‐down control by piscivorous fish. Objectives From 2020 to 2023, eutrophic, cyprinid‐dominated Lake Skjoldenæsholm (Denmark) underwent an integrated restoration program to establish a missing piscivorous food‐web component. Methods Interventions combined aluminum‐based P inactivation, intensive manual removal of cyprinids, and stocking of large (>15 cm) wild piscivorous European perch ( Perca fluviatilis )—a measure rarely documented in lake restoration projects. Water quality, fish community composition, and macrophyte colonization were monitored throughout the interventions and in the following year (2024). Results Water quality improved markedly following the combined effects of P inactivation and food‐web manipulation. The fish community structure shifted from dominance by small, young‐of‐the‐year (YOY) roach to one increasingly characterized by perch of various sizes and fewer, larger roach. Conclusions The decline in roach YOY suggested reduced recruitment and/or strong perch predation, while increasing perch abundance likely reflected both successful stocking and reduced competition following cyprinid removal. This demonstrates how successive interventions—internal P load control, fish removal, and piscivorous perch stocking—can rapidly improve water quality, balance fish communities, and promote macrophyte recovery in shallow, eutrophic lakes. However, greater knowledge of the factors that ensure high post‐stocking survival and overall efficiency of stockings should be prioritized to develop species‐specific stocking guidelines.