Each year, Saprolegnia infections of farmed salmonids and their eggs cause production losses estimated at tens of millions of euro worldwide. At present, there is no efficient treatment available. In vitro activity of ten chemicals and three commercial products was tested on different strains of Saprolegnia, using malachite green as reference. The compounds were screened in agar and in water to assess their minimum inhibitory concentration (MIC) and their minimum lethal concentration (MLC), respectively. The agar tests show that most of the compounds tested considerably slowed mycelial growth and/or inhibited development of Saprolegnia spp. after 6 days although at different concentrations. In water tests, iodoacetic acid showed the lowest MLC, however, acetic acid and peracetic acid‐based products, in combination with hydrogen peroxide, represent promising candidates due to their effectiveness associated with low environmental impact. In particular, while in agar the commercial products tested (VirkonS™, Detarox®AP and Actidrox®) were effective at 1000 and 500 ppm, in the tests in water the activity of Detarox®AP and Actidrox® was considerably enhanced (MLC at 100 and 500 ppm).