Preserving the natural values of the Ipoly/Ipeľ, a river forming part of the Hungarian-Slovak border, cannot stop at national borders. This was highlighted by a case submitted to the #ACCESS Help Desk and by an expert consultation initiated by the Danube Strategy National Coordination and held on 24 July 2026, which focused on the protected Danube mayfly (Ephoron virgo) and the artificial lighting of bridges along the Ipoly/Ipeľ.

An important part of the Danube mayfly’s life cycle is its late-summer swarming. Artificial light, however, can disrupt the mayflies’ natural behaviour: lighting on bridges and along riverbanks can create what is known as an ecological trap, causing large numbers of swarming insects to die before they are able to reproduce successfully. The issue goes beyond the protection of a single species: the Danube mayfly plays an important role in the river’s food web, while its larvae also contribute significantly to ecological processes in the riverbed. In recent years, researchers from ELTE and the HUN-REN Centre for Ecological Research have developed an optical system that can be installed on bridges and functions as a so-called mayfly-protection light barrier, preventing the formation of such ecological traps. Similar systems are already operating on several bridges in Hungary, with installations on additional bridges currently under preparation.

In the case of the Ipoly/Ipeľ, a cross-border approach is particularly important. Eight bridges along the river are currently known to be relevant to the assessment; five are managed by Hungarian authorities and three by Slovak authorities. According to experts, interventions should not be limited exclusively to river sections where the presence of the Danube mayfly has already been confirmed, as the species may also occur in other suitable habitats and its distribution may change over time.

Nature conservation measures are important in themselves, but in the case of the Ipoly/Ipeľ, their cross-border dimension poses an additional challenge. The river and its ecological processes do not follow national borders, while the bridges concerned are managed by different countries and institutions. Coordination is therefore important not only among authorities with different competences within each country, but also across the national border—an area in which the #ACCESS project can provide support. The protection of the Danube mayfly is a good example of how cross-border cooperation can be relevant not only in transport, public services or public administration. When it comes to protecting shared natural systems, achieving lasting results is difficult without cooperation between institutions operating on both sides of the border.

Protecting the Danube mayfly along the Ipoly/Ipeľ may develop into a complex task combining nature conservation and cross-border cooperation, involving the management of legal and administrative obstacles, the coordination of scientific knowledge and monitoring data, as well as concrete infrastructure interventions. Such cooperation can help ensure the long-term preservation of the natural values of the Ipoly/Ipeľ’s shared ecological system, while also strengthening the practical framework for cross-border nature conservation cooperation between Hungarian and Slovak institutions.