A　surface-enhanced　Raman　scattering　(SERS)　substrate　with　good　flexibility　and　high　water　absorbing　capacity　is　reported.　It　consists　of　a　calcium　alginate　sponge　incorporating　gold　nanoparticles.　These　are　in　close　contact with　the sponge　without　the　need　for　amino　or　sulfhydryl　modification.　The　substrate　is　capable　of　detecting　the　dyes　crystal　violet　(CV)　and　malachite　green　(MG)　in　water　directly　and　rapidly　by　immersing　it　into　the　liquid　sample.　Preconcentration　and　separation　are　not　required.　The　dyes　absorbed　on　the　sponge　can　be　detected　without　drying　and　thus　the　whole　analytical　process　can　be　completed　within　3 min.　The　results　show　that　the　lowest　detectable　concentrations　are　0.1　and　0.25 μg⋅L−1　for　CV　and　MG,　respectively.　This　is　lower　than　the　minimum　required　performance　limits　set　by　the　European　Commission　and　the　US　EPA.　Moreover,　MG　and　CV　can　be　simultaneously　detected　in　liquid　samples　due　to　their　different　SERS　bands　(at　1216　and　1534 cm−1,　respectively).　It　should　be　noted　that　the　molecular　structures　of　MG　and　CV　are　very　similar.　Therefore,　the　method　has　a　large　potential　for　determination　of　several　analytes　simultaneously　even　in　complex　sample　metrics.　[Figure　not　available:　see　fulltext.].　©　2019,　Springer-Verlag　GmbH　Austria,　part　of　Springer　Nature.