so many dead fish you could barely see the water behind lisa marie sander's harbor home. >> more than all the fish you see is the worry that its to take so long for it to come back. for the ecosystem to come back. >> it's tragic. >> cocoa beach mayor says evidence of the massive fish kill started floating up along the residence waterfront homes on friday and since then local and state wildlife officials sampled the water and collected dead fish for testing. >> they haven't identified it yet. so we are in early stages of determining what caused it and prior to that, i mean, we don't know what we are going to do. >> one possible cause is brown tide. according to the st. john water management district which in january confirmed a growing presence of the oxygen-depleting algae. it's turned the river brown and if concentrating enough can cause massive fish kills. >> they can come and go within a few weeks or last many months as >> if brown tide is confirmed they say the algae must run its course. they blame decades of storm run off which includes lawn fertilizers and pesticides. in areas l