Algal　blooms　in　lake　and　reservoir　water　lead　to　water　quality　problems,　including　water　odors,　algal　toxins,　and　disinfection　byproducts.　A　novel　dissolved　air　flotation　process　that　incorporates　positively　charged　bubbles　(PosiDAF)　can　effectively　remove　algae　in　lakes　and　reservoirs.　Chitosan,　as　a　modified　bubble　agent　in　the　PosiDAF　process,　has　attracted　extensive　attention　due　to　its　natural　nontoxicity　and　good　flocculation　proper-ties.　In　this　paper,　three　types　of　amphiphilic　chitosan　with　different　lengths　of　carbon　chains　were　prepared　via　amphiphilic　modification　and　were　used　as　bubble　modifiers　to　remove　microcystis　aeruginosa　in　the　PosiDAF　process.　The　effects　of　algae　removal　under　different　dosage　of　modifiers　were　compared,　and　the　role　of　algal　organic　matter　was　investigated.　Results　showed　that　the　water　solubility　of　chitosan　was　markedly　enhanced　after　amphiphilic　modification,　while　thermal　stability　were　decreased.　When　using　butyl-N-2　hydroxypropyl　trimethyl　chitosan　ammonium　chloride　(C4-HTCC),　the　effect　of　modified　air　flotation　was　the　best,　and　the　removal　ratio　of　algae　was　93.47%　when　the　C4-HTCC　dosage　was　1.0　mg/L.　The　presence　of　AOM　enhanced　the　overall　effect　of　algae　removal,　and　electrostatic　attraction　was　the　primary　adhesion　mechanism　of　the　microbubble-amphiphilic　chitosan-algal　organic　matter-algal　cell　system.　In　addition,　adsorption　bridging　and　net　trapping　also　have　positive　effects　on　algae　removal.