Abstract: Purpose – This study aims to monitor seawater by determing two biological indicators, Escherichia coli and Enterococcus faecalis. The process of following standard procedures is mainly time-consuming. Thus, there is a demand for a biosensor, an appropriate device for rapid and accurate results that can give information about the microbiological quality of seawater in an effective and rapid way. Design/methodology/approach – In the gold standard method for seawater monitoring, the filter method is applied as a condensation step. In this work, the authors evaluated six types of common syringe filters for bacteria concentration and then the best filter was used for seawater analysis for E. coli and Enterococci with loop-mediated isothermal amplification (LAMP) polymerase chain reaction (PCR). Findings – Cellulose acetate filter had the highest efficiency (98%) for bacterial concentration. The limit of detection of the LAMP method was 104/1,000 mL for both E. coli and E. faecalis. The proposed method could be used for the development of seawater biosensors with advantages such as a simple heating element and the speed that the LAMP PCR presents. Originality/value – The suggested protocol is proposed in an integrated in situ system, a biosensor, for seawater quality determination.