Arsenic and Mn levels in Isaza (Gymnogobius isaza) during the mass mortality event in Lake Biwa, Japan

► Mn and As levels were significantly higher in MMI than in NFI. ► The number of chemical species of As detected from MMI was less than that from NFI. ► Mn and As levels were highest in surface sediment, and sharply decreased with depth. ► Mn and As levels in surface sediment temporally increased.