colors colours danger decay environment environmental environmental problems harm harmful lake lakeside pollution Slime slimy sludge water weeds waterways weeds black brightly-coloured carpeting-plants clump-forming clumps common daisy-like drought-tolerant environmental-weed flower flowers garden flowers garden-escape gazania gazanias golden hardy introduced-species invasive lance-shaped leaves low-growing orange perennial plants prolific rapid-spreader resilient roadside-weeds South-African streaked tough vivid water-wise weed widespread wind-blown seeds yellow brightly coloured carpeting plants environmental weed garden escape introduced species rapid spreader roadside weeds South African abstract algae background bacteria bacterium bog canal fen goo gooey green grunge grungy marsh mat nature plant poison poisonous pond scum stagnant swamp texture thick toxic water wet brown color coloration colored colorful colour coloured colourful contrast contrasting garden-flowers wind-blown-seeds winter lance-shaped-leaves appearance