A regional administrative bench in Thessaloniki on Friday halted work on a proposed channel at the Amvrakikos Gulf, giving authorities six months to reassess its effects on the wetland. The ruling turned the field notebooks of Leon Holzer, a 71-year-old retired naval hydrographer, into a central piece of evidence in a dispute over where the lagoon’s water comes from.
Holzer’s 9,416 readings, taken between 1998 and 2025 near the village of Vonitsa, show water levels rising at times when tides and rainfall alone would not explain them. A research team says the pattern points to a freshwater seep beneath the salt flats. The judges did not rule that a spring exists, but said the project’s environmental review had failed to address the possibility.
The notebook behind the ruling
For years, Holzer recorded the level and salinity of water around an old harbour gauge, often before dawn. He had been tracking conditions for small-boat moorings, not conducting a conservation study. When the gauge stopped working, he kept using a marked timber post and a hand-held salinity meter, writing each result in pocket books stored at his home.
“I was trying to tell fishermen whether their ropes would go slack,” Holzer said in an interview beside the lagoon. “I never thought anyone would use those pages to decide what happens to the marsh.” His notes were presented during an appeal by local residents and a bird-protection group against plans to deepen a 2.7 km (1.7-mile) drainage channel.
I was trying to tell fishermen whether their ropes would go slack. I never thought anyone would use those pages to decide what happens to the marsh.
Leon Holzer, retired naval hydrographer
The proposed channel is intended to move excess water away from farmland after heavy winter rain. Its supporters say it would reduce crop losses and keep access roads passable. The ruling does not cancel the project, but work cannot begin until planners assess whether faster drainage could lower lagoon levels or alter the mix of fresh and salt water.
A pattern beneath the salt flats
A team led by marine hydrologist Natasha C. Motloung compared Holzer’s readings with satellite images and 34 water samples collected over two summers. In several dry spells, the gauge recorded a rise in water level alongside a drop in salinity. The team’s preliminary analysis, submitted to the bench, identifies a likely underground inflow; it has not yet mapped its source.
Motloung said the notebooks were useful because they covered years when official monitoring at the site was intermittent. “They are not a substitute for a modern network of sensors,” she said. “But the repeated changes are consistent enough that an assessment should test for groundwater before it approves a channel that could alter the lagoon.” Her team plans another sampling round in spring.
The area supports fish nurseries and seasonal bird-feeding grounds, while nearby farms depend on drainage to protect crops. The local water office must now commission a revised assessment and publish its findings before the bench will reconsider the permit. Holzer says he will hand over the original notebooks for scanning, but plans to keep one: the first, he said, still has salt stains on its cover.
