I'll take exception to your lexicon! A flounder is actually a very agile swimmer! To FOUNDER is an old nautical term meaning to tip, sway and otherwise not sail very well!
I think you've been tripped up by public language ignorance!
John Kuthe...
floun·der1
/ˈfloundər/
verb
verb: flounder; 3rd person present: flounders; past tense: floundered; past participle: floundered; gerund or present participle: floundering
struggle or stagger helplessly or clumsily in water or mud.
"he was floundering about in the shallow offshore waters"
synonyms: struggle, thrash, flail, twist and turn, splash, stagger, stumble, reel, lurch, blunder, squirm, writhe
"people were floundering in the water"
•struggle mentally; show or feel great confusion.
"she floundered, not knowing quite what to say"
synonyms: struggle, be out of one's depth, have difficulty, be confounded, be confused; More
informalscratch one's head, be flummoxed, be clueless, be foxed, be fazed, be floored, be beaten
"she floundered, not knowing quite what to say"
•be in serious difficulty.
"many firms are floundering"
synonyms: struggle financially, be in dire straits, face financial ruin, be in difficulties, face bankruptcy/insolvency, founder
"more firms are floundering"