Sri Lankan Navy detained four Indian fishermen near Delft Island on Tuesday morning.
The Lankan Navy also seized one country made boat which was allegedly used for poaching in the Sri Lankan territorial waters.
All the fishermen have been taken to Kangesanthurai Naval Camp and are likely to produce Jaffna fisheries later in the day.
Straying of Indian and Sri Lankan fishermen into each others' waters is a recurrent problem as territories on the sea are not clearly demarcated.